The stage directions say only, "They kiss." Getting there is something else: Picture Amy Irving and Chris Noth tangled in microphone cords, encumbered by bulky headphones, hands fumbling to turn the page.

Then the leading man's stomach growls so loudly that the entire production staff cracks up smack in the middle of Noth's marriage proposal.

Luckily, this is only a rehearsal. When this production of "The Heiress," an adaptation of Henry James's "Washington Square," premieres tonight, the kiss should sound just right -- a hesitant but lustful event, a moment of destiny and self-discovery for a shy, not terribly attractive heiress.

How the kiss looks is almost immaterial. Even though "The Heiress" will be performed before an audience at the Voice of America Auditorium on C Street SW, this is radio theater, being recorded for broadcast worldwide on the VOA, nationwide on National Public Radio and locally on WETA (90.9 FM).

So the kiss has to sound like, well, not necessarily like a kiss, but something a listener's imagination can turn into a kiss.

"Just play the moment," director Nick Olcott tells Irving and Noth as they rehearse the scene for the eighth time in 30 minutes. "Have the pleasure and we'll take whatever scraps of sound we can. Don't worry; doing it will change the quality of your voices. The listener will be able to figure it out."

But after the next try, the sound technician says there's not enough kiss on tape. Listeners might not know. So Olcott ratchets up the kiss.

"We're talking a Merchant-Ivory kiss here," he tells the actors. "Real ardor. You don't lead with the tongue."

And on the next take, Noth and Irving step toward the same standing microphone, recite their lines, pause, and the silence swells as it can only on radio. One second, then another, and then the tiniest trace of smoochery, a couple of hurried inhalations, the slight sound of lips rubbing against one another, a rich exhalation, and finally the play's words resume.

"Magnificent," the director proclaims. "That's the magic of drama." Staging a Comeback

There's not much call for radio drama these days, at least not in this country. Radio theater never went completely out of fashion in Britain, but in the United States, it was quickly and almost entirely silenced by television.

What was once the primary form of mass entertainment was relegated to nostalgia broadcasts and quaint museum productions. But radio theater is making something of a comeback, on public radio and in cassette sales, winning new listeners as a corollary to the books-on-tape craze. One of the most active radio drama producers, L.A. Theatre Works, has brought its show to Washington for a series of three productions sponsored by Smithsonian Associates,the Voice of America and several local theaters.

For actors, it is a welcome chance to exercise what is traditionally their most important tool -- and what has become almost entirely neglected in a movie- and TV-dominated environment -- their voices.

"I spent five years playing a New York homicide detective on Law & Order,' and it's three years of speech at Yale School of Drama right out the window," says Noth, who played Detective Mike Logan on the long-running NBC cop show. Now, in his first radio play ever, Noth is juiced as he hasn't been in years.

"We've become such a visual culture," he says. "We don't think about diction. Now, I stand up there with the headphones on and it gives the play such incredible intimacy."

Listen to the actors with a pair of phones and you hear them as one would on the radio -- Irving's impossibly soft consonants floating like feathers over the slight throatiness that lends her characters their innocence and vulnerability; Irving and Noth trading the quickest of breaths as their romance heats up.

"We really get to eavesdrop," Olcott says. "We're not observers as we are of a stage play. It's happening inside our heads."

To hear top-notch actors focusing on their voices is to notice what's missing from so many movies and TV shows. "Voices have gotten so flat and uninteresting," Olcott says. "There isn't much attention to sound and timbre and articulation."

Oddly enough, it is in advertising that voice still makes the sale. Listen in your mind to Donald Sutherland's masterful monotone on those Volvo spots, his instantly recognizable voice commanding attention with just a trace more than a whisper. Think of all the Burgess Meredith imitators trying to lend ads some of the late character actor's growly gravity. Consider the omnipresence of James Earl Jones's stately diction.

In the quick-cut world of TV advertising, voice is the only tool those actors have. So it is in radio theater.

"It's a completely different discipline," says Irving, who has been working with L.A. Theatre Works for a decade, playing with such actors as Richard Dreyfuss, Joe Mantegna and John Lithgow in works by playwrights from Shakespeare to Arthur Miller to Neil Simon. "You can hear your own voice through the headphones. And everyone else's voices are right in your head. It's very intimate." A Cleansing Experience

Rehearsing a radio production, Olcott says, "is like taking all the boring parts out of the schedule. We don't have to wait for the actors to learn their lines, or for the set to be built."

That's part of the attraction for the actors, who are paid minimally and who recognize from the start that the audience will be small, the notice slight.

"The time is shorter," Irving says. "I'm here Monday through Friday and that's it. You don't have to learn the lines. You can't even look at each other because you have to stay on mike."

It is an acting experience of rare, personal purity -- no accountants, lawyers or overbearing executives cluttering up the set, no casting decisions driven by focus group studies.

"You do this because the actor in you needs it," says Noth, who is working on an HBO series, "Sex in the City," but longs to work in the far less remunerative theater. "After five years on the TV show, I salted enough away so I don't have to do a terrible movie or miniseries. I really want to reach the point where I don't have to do any TV. Acting is so much more fun when the writing's not awful and it's not all cliches. Doing theater, or radio theater, is a cleansing experience. You have the feeling of doing a good day's work."

The Washington radio theater series continues in March with Arthur Miller's "All My Sons," starring Julie Harris and Charles Durning, and in April with Studs Terkel's "Working," featuring Kelsey Grammer.

"You can play anybody in radio," says Irving, whose most recent films are Woody Allen's "Deconstructing Harry" and Herb Gardner's "I'm Not Rappaport." "Roles you might have missed, you can go back to. Roles you're too pretty for, too old for. It doesn't matter how you look, just whether you can modulate your voice."

For her role as Catherine Sloper, the New York heiress who frightens her domineering father by falling for the fortune-hunter Morris Townsend (Noth), Irving scales down the size of her husky voice while raising its tone to insinuate innocence. As the character grows into herself, Irving's voice grows firmer.

"It's a chance to expose yourself to as much theater as possible," the actress says. "You just listen to the music of each playwright and sing it in the right key."

A few tickets remain for tonight's performance of "The Heiress"; call 202-357-3030 for information. Tomorrow's show is sold out; tickets remain for the March and April productions. WETA will broadcast the radio plays at a date to be determined. CAPTION: "Just play the moment," director Nick Olcott told Amy Irving and Chris Noth as they took another shot at a kiss for Voice of America's "The Heiress," a play based on Henry James's "Washington Square." CAPTION: A growling stomach prompts laughs from Amy Irving and Chris Noth at rehearsal.