KAUFMAN and Hart had lunch at the Watergate the other day.

Hart wore a full-length mink for the occasion and Kaufman sported a fancy blouse. They traded anecdotes and swore that they're as close as sorority sisters.

A photographer dropped by to snap the pair, and the dialogue went like this:

Hart: You're upstaging me, kid.

Kaufman: I wasn't born yesterday.

Hart: Chin up!

Kaufman: I've got my chin up. You just can't tell because I'm wearing ruffles like you told me to.

Hart: Now smile!

Kaufman: If I say we're sold out this afternoon, that ought to do it.

(Broad smiles all around.)

Kaufman and Hart, in this instance, happen to be Anne Kaufman Schneider (adopted daughter of the late George S. Kaufman) and actress Kitty Carlisle Hart (widow of Moss Hart). The original Kaufman/Hart collaboration produced three of the most enduring comedies in the American theater ("You Can't Take It With You," "Once in a Lifetime" and "The Man Who Came to Dinner"), not to mention a handful of lesser works ("Merrily We Roll Along," "George Washington Slept Here," "The Fabulous Invalid"). The latter-day Kaufman/Hart watch over them like children. Holding the rights to those plays, as they do jointly, is more or less the equivalent of having a functioning oil well in the backyard.

In an average year, there are approximately 1,000 stock and amateur productions of "You Can't Take It With You" across the country, making it one of the most frequently performed of all American plays. Add the other Kaufman/Hart comedies, and you're talking about 2,000 productions. Tote up the royalties--$35 here, $50 there--and the annual revenue hovers around $100,000.

This, however, is not an average year. "You Can't Take It With You" is once again heading for Broadway in a loving revival directed by Ellis Rabb, and if Washington is any measure, the oil well is about to start gushing all over again. During the tryout here in the Eisenhower Theater, attendance quickly built to capacity. The final week of performances, starting today, has long been sold out. With the weekly grosses running approximately $160,000, the Kaufman/Hart (or Schneider/Carlisle) team finds itself richer by $13,000 every seven days.

"We're the keepers of the flame," says Carlisle, graciously. "By that I mean that we don't allow first-class Broadway productions to be done unless we're sure . . ."

". . . they're going to be first-class," interrupts Schneider, clearly the more pragmatic of the two. "We have approval over the director, the cast, the designers."

In other words, if these women say no, there's no revival.

What they've learned over the years is that to make old plays into new hits you need a little extra something. "You can't just put them on well with competent actors," says Schneider. "You've got to bring an added dimension to them. Ellis understands this so well. Take his revival of 'The Royal Family,' which my father wrote with Edna Ferber, although everyone thinks it's by Kaufman and Hart. To watch Eva Le Gallienne drift down the staircase and realize that you were seeing her life on stage as well, that was the added dimension. I think Ellis understands 'You Can't Take It With You' in a way that Moss and my father never did. He understands the sentiment in it. My father would have been afraid to lose the laughs. But it really is a play about a warm family that loves and accepts one another."

Carlisle: "There was no sentiment in it originally. George and Moss never saw that. They thought of themselves as commercial Broadway playwrights. They had no idea of having written a classic. Sometimes Moss would say, a little wistfully, that Arthur Miller was viewed as the real thing, not he and George. And I'd say, 'Well, wait, you two may yet become the Beaumont and Fletcher of your time.' "

Schneider: "And they have. But they really thought they were just writing this crazy comedy about a funny family. My father was very diffident about himself. Strange and oddly diffident. Ours was an extremely disciplined household and the tolerance level was very low--nothing like the Sycamores in 'You Can't Take It With You.' I think if Moss could wake up for a moment, I think he might say, 'Kitty, you were right. It happened.' My father would be flabbergasted. He wouldn't believe that his play was selling out on a Thursday matinee in Washington. He'd want to know why there aren't other people writing."

By common agreement, most of the business of the Kaufman/Hart estate falls to Schneider, although both of them make a point of seeing every major Kaufman/Hart production in America. (Schneider also takes in the European productions.) Actress and longtime television panelist on "To Tell the Truth," Carlisle is now chairman of the New York State Council on the Arts, a job that monopolizes her time.

"She's the classy one," says Schneider. "I'm show biz. It's very easy to tell us apart. We're very much like our respective father and husband. Kitty is nice and loving and fun and pretty. I growl. Kitty laughs. I'm a crier. Really, I cry at card tricks. I'll tell you another difference between us. Ellis first revived 'You Can't Take It With You' in 1965. I was at a tacky opening night party when the raves came in. So I phoned Kitty to tell her the good news. She was dining with Princess Margaret."

Carlisle, the laugher, is laughing.

The two first crossed paths in Hollywood on the set of the Marx Brothers movie "A Night at the Opera." Kaufman, who was the dialogue coach on the film, brought his daughter by one day to observe shooting. Carlisle was playing the ingenue and sang "Alone," although neither seems to remember much else. They didn't really get to know one another until the Kaufman/Hart collaboration was going strong in the 1930s and their respective families had moved to Bucks County, Pa. Living next door to one another, the playwrights had a habit of pooling their celebrated weekend guests.

Now Carlisle and Schneider phone each other at least twice a week--more when there's a business deal afoot. "Kitty has two Spanish maids, so I've had to learn Spanish in order to be able to leave messages," says Schneider. At the Kaufman/Hart revivals, they invariably sit together, hold hands and cry--not always in pleasure.

Careful as they try to be, they admit to making a whopper of a mistake by authorizing a musical version of "Merrily We Roll Along" last season.

Carlisle: "When Steve composer Stephen Sondheim and Hal producer/director Harold Prince told us the idea--that they were going to do it with 18-year-olds--my eyebrows shot right up to my hairline. I thought it the worst idea I'd ever heard. But who were we to say?"

Schneider: "Well, we had to make a decision. Either say no right there or turn over control to Hal and Steve."

Carlisle: "Yes, but it seems to me they went to such lengths . . ."

Schneider: ". . . to find untalented, unattractive people."

Carlisle: "It was disastrous."

A successful Broadway revival, however, can have a significant ripple effect--reawakening interest not merely in a specific Kaufman and Hart work, but the oeuvre as a whole. It can even spill over onto those plays Kaufman and Hart wrote separately or with other collaborators. Currently there's talk of "The Solid Gold Cadillac" (Kaufman and Howard Teichmann) for television, a medium both women scorn. And there has been theatrical interest in "Light Up the Sky" (Moss Hart alone). "You Can't Take It With You," if it's well-received in New York, could speed both those projects along.

More is at stake, however, than the protection of valuable theatrical property. Both women, who will drop a quip into the first available hole in the conversation, believe in the ultimate seriousness of their mission.

Says Carlisle, "When I was young, my mother took me to Europe. She wanted me to marry a prince, hopefully a rich prince or failing that, an impoverished baron. Well, I blew it and we lost what little money we had. So we came back to the States and I went to work right away in vaudeville. But in a way, my mother was right. I did marry a prince. He was a prince of the theater. And now keeping Moss' name and his plays alive in people's minds is very important to me."

Adds Schneider, "I feel very much the same way, but I didn't realize it until fairly recently, when I started seeing the plays in Europe. I was very moved by the fact that they work the same way everywhere. In Amsterdam or Oslo or Bratislava. Even where they have no frame of reference for these particularly American comedies, audiences laugh in all the same places. And I realized that immortality, if there is such a thing, only comes from living people. It's passed along. It's remembering. So I try to get these plays done everywhere."

Both looked uncharacteristically grave for a moment. Then Kaufman and Hart polished off their tea and checked their makeup and headed off to a sold-out theater--their mission, for the time being, accomplished.