She is a knockout blonde who introduces herself as Maddie Hayes; he is a cocky guy with a rhythm and blues soul named David Addison. The letters are from people who write things like: ''I read somewhere that you and Maddie were going to kiss and have a big affair. Is this true? If it is . . . can you tell me when so I can set my VCR?''

The leading man doesn't tell his audience he's an actor, named Bruce Willis, playing a role. ''See,'' he insists, ''I'm just a television character. I can only tell you what's going to happen tonight. We don't kiss tonight.'' ''You said not tonight?'' asks the leading lady, the former high-fashion model Cybill Shepherd who plays former high-fashion model Maddie Hayes.

''Definitely, I read the script,'' he replies. ''Not tonight.'' But on this show, even randy television characters have minds of their own. ''I feel stupid,'' David says to Maddie. ''I don't know what we're waiting for.'' ''But it's not in the script,'' Maddie coos.

''C'mere,'' David snarls playfully.

And, as the script would have it: ''She does . . . their lips draw closer . . . and they FREEZE . . . .'' After a moment, they agree that something is wrong. Suddenly, the screen goes black and we hear their voices in the dark:

She: I always thought there'd be romantic lighting . . . and music.

He: Really?

She: Really.

He: Well . . . I'm not as fussy as you are about these things . . .

She: Lights!

The real kiss would be slipped into an episode two weeks later, almost as a tease, with Maddie saying to David ''C'mere stupid.'' But after they kissed, they both agreed that it hadn't happened because they said it hadn't happened. And so it goes on ''Moonlighting.''

The madcap creation of executive producer Glenn Gordon Caron, ''Moonlighting'' is an anomaly in television. Not only is it a detective show that is weak on action and long on dialogue, but it is also the only hourlong comedy in prime time - and one of the most expensive series. Edged by its creator with a dark border that is evocative of the film-noir genre of the 40's, its dual identity wasn't lost on the the Directors Guild of America, which nominated one episode for best comedy and one for best drama, an unprecedented occurrence in the guild's 50-year history. Earlier this month, one of the show's directors, Will Mackenzie, won the guild's award for best director of a prime-time drama. Cybill Shepherd and Bruce Willis won the People's Choice award as favorite performers in a new television series, as determined by viewer votes. And there is talk about several Emmy nominations.

Though ratings were lackluster last March when it premiered, ''Moonlighting'' has become one of ABC's highest-ranked series and has helped the network to edge out its competition on Tuesday nights. So varied is the show's cult following that it inspired actress Whoopi Goldberg to request and receive a guest-star role in an episode that will air in May as well as prompting comedienne Imogene Coca to call Caron and insist that she is the mother of the show's bug-eyed receptionist, Ms. DiPesto. It also made a fan out of the erudite Mexican novelist Carlos Fuentes, who in a recent interview said: ''Who isn't in love with Cybill Shepherd on 'Moonlighting' these days? . . . She is the only actress who . . . makes you think of Carole Lombard and those zany actresses of the 30's. It's a very well-done show . . . .''

At its best, ''Moonlighting'' speaks from the heart - of jealousy, sibling rivalry, infidelity, faith - against a backdrop of humor and pop-culture references ranging from the Temptations to ''Family Feud.'' Paying tribute to one of the most successful paradigms in American film - the sparring couple whose antagonistic dialogue is thick with romantic subtext - Glenn Caron has given it an 80's twist with Maddie and David, whose fast-talking, wisecracking repartee is the bittersweet soul of the show. If Maddie and David aren't disagreeing on the existence of God, they may be arguing the relative merits of Gauguin and Renoir. Or piling triple upon double entendres. But the zaniness isn't solely verbal. One week, the heroes may overcome their armed foes by zinging Frisbees and toy cars at them; the next, a wild hearse chase ends up at a baseball diamond with a coffin rolling out onto second base and David yelling to it, ''You're safe!''

Maddie is a steely but gorgeous model who was bilked out of her fortune by a business manager and forced to make good on her tax-write-off of a business, the Blue Moon detective agency. David, her unlikely partner, is a lascivious male chauvinist with a crooked grin whose motto is, ''Live Fast. Die young. Leave clean underwear.'' Like Burns and Allen or Hope and Crosby, they often break the ''fourth wall'' with a wink at the audience, admitting they exist within a 19-inch frame. It is a device that amuses Caron, who is scheming to have a character strike a match on the edge of the screen.

But Caron is the first to admit that his show pays a price for what New York Times television critic John J. O'Connor called ''the courage of its offbeat goofiness.'' While most television series finished shooting this season's shows weeks ago, ''Moonlighting'' is still in production. While most scripts run 60 pages for an hourlong show, those for ''Moonlighting'' are nearly twice that long because its characters talk so fast. While the average television show may take seven days to shoot, ''Moonlighting'' sometimes takes 12, even 14. While most television shows have scripts ready weeks before filming begins, ''Moonlighting'' episodes are frequently being written by Caron the same day they are shot. A tongue-tied staff writer offers his insight into Caron's administrative skills by borrowing the theme song from ''The Twilight Zone.'' ''Doo-doo-doo-doo,'' he sings. ''Welcome to the Caron Zone.''

THE PRODUCTION offices of ''Moonlighting'' at 20th Century-Fox in West Los Angeles are housed inside Building 38, a two-story gray structure that resembles a rundown motel from a Sam Shepard play. Upstairs in a corner office, near an abundant supply of Oreos and bagels and cream cheese, Glenn Caron tinkers at an I.B.M. typewriter. It is here, in an office decorated with family pictures, a jukebox and a punching bag, that he can usually be found writing up to the minute the cameras roll.

''Artie, tell me if this is funny,'' Caron says to his supervising producer, Artie Mandelberg, as he emerges from behind his typewriter. He has just finished dashing off a new opening sequence to fill three minutes of air time in the episode then in production, which is ''ridiculously short'' because of the fast-paced dialogue. As far as Caron is concerned, the show's opening will be launched out of ''Desperation City.''

Pacing outside his office and bouncing ideas off anyone who ambles by, Caron reads his new pages of material. The voice is Long Island; the delivery brisk, bordering on manic. ''O.K., so we're bombing here,'' he says, noticing that Mandelberg is not laughing. ''Wait a minute. It gets stranger.'' The stranger part is what will eventually air as the reading of fan mail.

''Moonlighting'' is Caron's dream come true, according to one of the show's directors, Peter Werner. As he puts it: ''I think this Long Island Jewish boy always had a fantasy blond shiksa'' - Gentile -''goddess. He also had an image of himself as being a fast-talking, wisecracking, down-in-the-street hustler. What he created was something out of the deep fantasy of his dreams. It's so much a part of his soul and he loves it so much that it works.''

At 31, Caron has the rumpled look of a preppy sumo wrestler and the persona of an oversized teddy bear. At once gentle and profane, he seems to enjoy, almost cultivate, the pressures of a ticking clock. His particular brand of mania is to wait till the last minute to write, shoot and edit his show. He calls the process ''stream-of- consciousness television,'' whereby the spontaneity and adrenaline generated offscreen seep onto the film. ''A certain amount of madness,'' he explains, ''is good for the exercise.''

So frenetic and exacting is Caron's pace that the music director may have to score his music to a blank screen, the writers don't know how a story will end as it's being shot, the directors have no time to prepare their pages, the actors learn lines on their feet while blocking them out and the crew is given daily call sheets that provide meaningless information, like ''T.B.A.'' - to be announced.

Caron's co-executive producer, Jay Daniel, who oversees the show's filming, says, ''We're just about as close as you can get to being live without being live.''

CARON VIEWS HIMSELF not as a writer so much as a balladeer, a storyteller, as in the name of his company: Picturemaker Productions. He looks at his show as a chance to make a ''little movie'' every week. Writing ''is just the thing that gets you there.'' What also gets him there is an able staff of five young writers: Roger Director, a columnist for Vanity Fair and a former ''Hill Street Blues'' writer; Ron Osborn and Jeff Reno, a situation-comedy writing team whose credits include ''Night Court'' and ''Mork and Mindy''; Debra Frank, an actress-turned-writer who had written for ''Cagney and Lacey,'' and her partner Carl Sautter, a former urban planner.

''Glenn loved three-fifths of our story, but he started to yawn when the slut comes in,'' Roger Director reports to the group.

''The secretary,'' corrects Debra Frank.

Meeting in a small conference room across from Caron's office, the staff writers are conferring with freelance writer Bruce Singer, who had originally pitched the idea for an episode about a visit from Maddie's mother. Out of that, Caron and his crew sculpted a three-line concept: Maddie's mother suspects her husband is having an affair. To prove her mother wrong, Maddie investigates. She winds up confirming her mother's suspicions. This premise enables Caron to expound on his notion of ''pretty lies - the quid pro quo of familial chess that if you buy my lie, I'll buy yours.''

The writing process on ''Moonlighting'' varies. Sometimes, staff writing is polished by Caron. Other times, Caron will write an episode by himself. Or freelancers wind up being rewritten by the staff, who in turn may be rewritten by Caron.

Now, the writers are critiquing Singer's first two ''acts'' and suggesting ways of propelling the story, to which Caron eventually affixes the fan-mail scene.

''What we're heading for is a third act break where Maddie has a silent confrontation with her father,'' explains Reno.

''As for the second act,'' Sautter adds, ''I think a stronger reaction than Maddie seeing her father kiss the other woman is David's reaction to Maddie's pain.''

For hours, the writers debate how the story's ''beats,'' or characters' emotions, should be played. Does it matter why the father is having an affair? Could the mother somehow be culpable? How best to reveal the affair without looking like an episode from ''Dynasty''? How can the story be played so that the situation sheds new light on David and Maddie's relationship?

The writers frequently lob one-liners at each other, as they grope for the emotional fabric of their characters.

''We haven't seen Maddie cry yet,'' Debra Frank suggests. ''I don't think knowing about the affair is cause for tears,'' Carl Sautter says.

Debra Frank asks whether Maddie couldn't be more like the heroine in ''An Unmarried Woman.''

''We haven't seen Maddie vomit yet'' is Roger Director's quip. '' 'Maddie Vomits.' Like 'Garbo Talks.' ''

BY THE TIME HE HAD WRITTEN 50 pages for the pilot to the show, Caron says, he realized he was writing for Cybill Shepherd.

''I had to have somebody the public was fundamentally rooting against,'' he says, ''because the show was about the thawing out of this beautiful ice queen. And I knew the public saw her as spoiled and bratty.''

As for the part of David, Caron says he and his casting scouts auditioned thousands of actors before Bruce Willis arrived from New York sporting a punk hairdo and earrings. But there was something in his attitude that was right. ''I think Glenn saw I could do his material,'' says the star, who had been bartending in New York before landing a role in the Off Broadway production of Sam Shepard's ''Fool for Love,'' ''and that I could stand up to Cybill and just say, 'Look, this is the way things are, honey.' ''

The undeniable chemistry that has developed between Cybill Shepherd and Bruce Willis is one of the staples of ''Moonlighting.'' ''When we're really cookin', it's weird,'' Caron says of his ensemble. ''It's almost like mind reading.''

Indeed, telepathy seems to play a central role in the show's creative process. ''I can read everything that goes on in his mind,'' says Cybill Shepherd of Caron. ''But I'm sort of a witch, you know. I get real clear signals from people.'' As Bruce Willis sees it, pointing to his head: ''It's funny, we just have that connection up here.''

Though the show has the feel of being completely extemporaneous, it's not. When an actor or director wants to change a single word of dialogue, the script supervisor must run to the set telephone to receive Caron's approval. More often than not, Caron will pad onto the soundstage in his scuffed penny loafers to debate the line in question. The real star of the show, it turns out, is the written word.

AFTER CANCELING SEVERAL writers' meetings over a period of weeks to work on another, more immediate episode, Caron rejoins his team to discuss Bruce Singer's first draft. Propping his feet up on the round conference table, his hands folded behind his head, he barely allows a line of the freelancer's script to pass unchallenged. If the previous meeting was free-flowing, even democratic, Caron is now the ringleader. There is neither room nor time for questioning his point of view.

No, Maddie will not investigate her father's extracurricular activities because it ''feels wrong.'' No, it doesn't matter why her father is having an affair; at the core of the show is Maddie's love for her mother. No, Maddie is not angry with her father for his betrayal so much as for his ''smugness'' about it. No, the confrontation between Maddie and her father must be stronger, physical. In the end, she will flail at him with her purse.

''We could do what other shows do,'' he tells the assembled group, ''and have people say what they feel. But I'm always suspicious of people who know what they feel. It's much more interesting when they don't know.''

In the weeks that follow, Caron transforms his anxiety about Maddie's tailing her father into two of the show's most moving scenes: David's offer to follow the father, and his subsequent revelation to Maddie, in a simmering, silhouetted night scene, that what her mother suspects is, indeed, true.

Although filming is scheduled to begin in three days, a first draft of the show's third and fourth ''acts'' has yet to be written. And Caron knows he will rework every page of the first two ''acts.'' Singer's script, initially titled ''The Family Hour,'' will be reshaped and retitled by Caron as ''Every Daughter's Father Is a Virgin.''

HI, EVERYBODY!'' Bruce Willis sings, boogeying down the hallway dressed in a clerical collar, porkpie hat and sunglasses and sporting a shiner his character will later explain away as having been acquired in a confessional.

It is 9 A.M. inside Soundstage 20, the first day of shooting ''Every Daughter's Father Is a Virgin,'' and, having been handed the first few pages of script minutes before, Willis is doing his best imitation of Archie Bell and the Drells' jive rendition of ''Tighten Up.'' The crew cracks up.

On the set, Caron is ubiquitous and fatherly. He rushes down the hallway before the scene is filmed to instruct Willis to dance first and then sing for his entrance, and is back on the soundstage minutes later to direct both his stars through a rehearsal of another scene he has just rewritten.

''On the cool quotient, isn't it cooler if you stay at the bathroom door?'' he asks Bruce Willis.

''But I don't know why I go to the bathroom,'' says the star, which sets off an unprintable exchange with Cybill Shepherd.

Caron ignores their banter. Rather than change the dialogue and direction in his script, he opts for a more impulsive choice. ''You want the truth?'' he asks, tearing up paper. ''Let's forget the next page.'' ''Yahoo!'' Willis shouts, ripping out a page from his script. ''We're back on schedule.''

An astute observer of others, Caron shields himself from close scrutiny with wry wit. At the same moment he grins and playfully tells you that everything is just fine as a writing deadline nears, he scratches the reddened skin on his forearms and then, looking embarrassed, rolls down his sleeves to hide a nervous rash.

For a man who creates what has repeatedly been called ''the hippest show on TV,'' he is surprisingly conservative. Save for the car phone in his Saab Turbo, he seems refreshingly unaffected by the trappings of Hollywood. His wife, Mary, says his idea of a big night out is staying at the Disneyland Hotel in Anaheim. Even his home, in the gated community of Hidden Hills, 30 miles north of Los Angeles, looks more like Ozzie and Harriet than David and Maddie - from the braided wool rugs littered with 3-year-old Matthew's Disney songbooks and 1-year-old Megan's teething rings to the Ethan Allen furniture.

The son of a knitting goods salesman and a window shade saleswoman, Caron grew up in a lower-middle-class section of Oceanside on Long Island. He chooses not to discuss his childhood now, except to say that his parents were divorced when he was a teen-ager.

Caron was very much influenced by his grandfather, who bought him a Brumberger crank projector when he was 6. In college, at the State Univer-sity of New York at Geneseo, he began writing screenplays. One of them was eventually read by a film production company executive who, upon moving to NBC, gave Caron a shot at writing the pilot for a television series called ''The God Squad.'' That show went nowhere; nevertheless, Caron's professional rise was meteoric, even by Hollywood standards.

He was only 26 when he adapted the film ''Breaking Away'' for a television series. After writing for ''Taxi'' and ''Remington Steele,'' he produced ''Concrete Beat,'' a failed series about a newspaper columnist. But he went on to sign a lucrative deal with ABC. Then ''Moonlighting'' clicked, due in large measure, he says, to his ''secret rabbi in the sky'' - Lewis H. Erlicht, former president of ABC Entertainment and now head of ABC Circle Films.

''Lew said, 'We really like what you do, but what you do is weird,' '' Caron recalls. '' 'Could you find a commercial genre in which to do it?' 'How 'bout a detective show?' I said, 'That's all America needs is another detective show.' But I very much wanted to write men and women. I said, 'What if it's a romance?' He said, 'I don't care what it is as long as it's a detective show.' ''

So far, ABC executives, who are expected to renew the show for next season, have granted Caron a surprising amount of freedom. The production costs of ''Moonlighting,'' for example, are extraordinarily high. The cinematic feel of the series - a highly stylized look that evokes the films of the 40's - prohibits the use of zoom lenses. Instead, moving masters -single cameras that move back and forth on railroad tracks - are employed. Since the dialogue between Maddie and David often overlaps, extra time and care must be taken by the sound mixer and editor to make sure that overlaps occur at just the right moment. To soften Cybill Shepherd's features, cinematographer Gerald Perry Finnerman relies on a ''spider'' glass diffusion disk which was once used for actress Joan Crawford. He also uses pieces of optical glass with one diffused and one plain side, so that in a two-shot, Maddie will be diffused and David will not be.

Equally important is Caron's obsession with keeping his dialogue intact over the objections of network censors at ABC's standards and practices department. ''We traffic in a certain amount of bad taste,'' he says. ''If they take that away, we don't have our show.'' His modus operandi appears to be to stall when dealing with network notes until Friday night after everyone has left the New York office and it is too late to make significant changes. Caron also knows that what is printed on the page - a play on words or innuendo - can play quite differently on film. So he offers network executives a chance to see what they're objecting to before a final decision is made, though usually not until the day before a show airs. Frequently, the network will retract its initial objections.

''In terms of operating a show, it's not the right way because there's no time to prepare and plan correctly,'' says ABC's Lew Erlicht. ''In terms of result, it's that extra attention to detail that gives the show its uniqueness.''

ROCKING BACK AND FORTH in a projection room chair, his face lighted only by the flickering images on the movie screen before him, Caron crunches on a pretzel stick and starts to recite some of the lines from ''Every Daughter's Father Is a Virgin.'' It is now, as he edits the raw footage, that he gets his ''last whack'' at polishing his actors' performances. Playing various characters, he jabs the air for emphasis, punching buttons on the control panel in front of him - for theatrical effect as well as to rewind a scene or fast forward it. His uninterrupted monologue, a steady stream of editing ''notes,'' bounds from frame to frame as he expounds upon his concept of the show, sandwiching his opinions between anguished sighs.

''Instead of making her happy,'' he says, ''hold on her, then - BANG! bring 'em back to the table. . . . Then, he says to his daughter, 'You enjoy your meal?' and she says, 'It was fine, Dad, fine.' Then I want a long, long, long, long pause. Then I want Mom to say, 'I did, too, dear.' . . . Yes on the bed. Lose the car.''

Chris Welch, a young editor-producer sitting behind Caron, dutifully scribbles notes in the dark. As he leaves the room to begin making editing changes, two more swollen-eyed editors arrive with yellow writing pads and lighted pens to jot down the rest of Caron's instructions. They, too, will be up all Saturday night editing the film, catering to Caron's creative passions.

''Well, dems da notes,'' Caron says as the lights in the screening room come up. His look of worry is mischievously transformed into a Cheshire cat grin. ''The insanity,'' he adds, as his weary film editors dart back to their workbenches, ''is just beginning.''

A BIG-BUDGET GAMBLE ''MOONLIGHTING'' is one of prime-time television's most expensive hourlong series. It is estimated to cost about $1.6 million per episode -compared to about $1.4 million for ''Hill Street Blues'' and ''Miami Vice,'' and $1.15 million for ''Remington Steele'' and ''St. Elsewhere,'' all NBC shows.

The show's high costs are due to executive producer Glenn Caron's longer, dialogue-heavy scripts and exacting production values, which require at least four more shooting days per show. The critically acclaimed black-and-white ''Moonlighting'' episode which spoofed the hard-boiled, film-noir movies of the 1940's, for example, is said to have cost about $2 million to produce. When television crews work past midnight on Friday and Saturday, they are normally paid double overtime, or ''gold time.'' The joke around the ''Moonlighting'' set is that they go into ''plutonium time.''

The economics of ''Moonlighting'' are unusual because it is owned by ABC, the third-ranked network purchased by Capital Cities Communications last year for $3.5 billion. (Only two other prime-time entertainment shows, NBC's ''Punky Brewster'' and CBS's ''Twilight Zone,'' are produced in-house by the networks.) ABC executives are willing to make a bigger investment in ''Moonlighting'' because the ultimate payoff for the network is the show's ''back-end potential'' - profits from the sale of syndication rights for reruns to local television stations and other outlets. Depending on market rates, a hit television show could make as much as $200 million in five years of syndication. CBS's ''Magnum, P.I.,'' for example, drew about $1.8 million per episode, and industry analysts expect that NBC's ''The Cosby Show'' will earn about $2 million per episode in syndication.

''That's the gamble the networks are taking these days,'' says Lew Erlicht, former president of ABC Entertainment and now head of ABC Circle Films, which produces ''Moonlighting'' with Caron's company, Picturemaker. ''We're trying to get the brass ring.''

Typically, a television series is made and financed by a film studio or independent production company, which leases its shows to the network for a licensing fee. The studios risk the cost of mounting deficits -between $300,000 and $500,000 per episode - before a series can be sold at a profit. In the case of ''Moonlighting,'' however, the network is the studio but it need not pay a licensing fee to itself. Thus, ABC executives look to ''Moonlighting'' as a kind of fiscal experiment.

''This is our test tube baby,'' says Sally Young, an ABC Circle Films production executive who oversees the show's budget. ''Nobody knows the answers yet. That's the beauty of being in third place. We may be breaking the rules, but that's following the rules of the industry. If your show is breaking creative barriers, it only follows you'll be breaking financial ones, too.''

Due to antitrust actions, broadcast networks are limited in the amount of prime-time programming they can produce in-house. In 1972, the Department of Justice argued that the networks were using control over access to eliminate competition in prime-time programming. The antitrust suits resulted in separate consent decrees in which the networks agreed to limit their in-house productions. ABC's settlement, signed in 1980, now allows it to produce up to three-and-a-half hours in prime time each week, including movies of the week and mini-series, increasing to five hours by 1990, when the decree expires. Already, ABC has sold the ''Moonlighting'' two-hour pilot as a home video in Britain and Scandinavia, says Archie C. Purvis, vice president and general manager of ABC Video Enterprises in New York. And the series has been licensed for syndication in Italy, West Germany, Britain, Japan, France, Mexico and Canada. Industry analysts suggest that the show in domestic syndication will be worth at least $1 million per episode. Says Purvis: ''We think we got ourselves a winner.''

-- JOY HOROWITZ