For Robin Williams, art doesn't imitate life so much as interrupt it all the time.

It's impossible to sit with Williams for more than two minutes without him suddenly taking a break and "going to movie"--creating whole scenes, characters, voices and gestures at the drop of a thought. It's entertaining, but is it life?

The other day Williams, a grown man, nearly 31, was in New York, in the Sir Francis Suite of the Drake Hotel, discussing his new movie, "The World According to Garp." It was as if somebody were switching channels on the tube.

He was recalling the first night of shooting, on the streets of Manhattan's Lower East Side. "They had all these extras," he said, "and some of the extras were supposed to be winos, like film winos, kind of elegant--they lean up against the wall but they caught their head at the right angle. And at one point a real wino showed up and started to whiz on the wall."

ASSISTANT DIRECTOR: (Panicked) That's not in the film!

SECOND ASSISTANT DIRECTOR: (Officious) Can I help you? What union are you in?

WINO: (Jumping up from the press table, facing a wall of the Sir Francis Suite, arrogantly talking over his shoulder) I don't need no damn union. ---- on your damn film.

ASSISTANT DIRECTOR: Jesus, get him out of here!

A few moments later he was explaining how he got the idea of playing Garp while reading John Irving's book on the Isle of Malta, where he was filming "Popeye." Shortly thereafter, someone gave him a shirt. "It was an army shirt, and on the shirt was a little tiny gold pin that said Garp on it."

TWILIGHT ZONE THEME: ni ni ni ni . . .

ROD SERLING: Mr. Williams. You're going on a journey beyond a one-eyed rubber sailor.

Robin Williams can do these improvised scenarios better and faster than any comedian since Jonathan Winters. Which at first presented a real problem to director George Roy Hill.

"The main thing George did with me was to cut away all the things I would normally want to do," explained Williams, "and to force me to just settle down, to a man who is deeply grounded. I mean, Garp is there, he's planted. He may do outrageous things, but he's not a man you see at a party with a lamp on his head."

MAN YOU SEE AT A PARTY WITH A LAMP ON HIS HEAD: How ya doin', Ted?

"And by doing that, he forced me to slow down my speech patterns. On many scenes he would say, 'Don't say anything, just shut up and sit. Relax and let things affect you.' Garp's more a reactor to things than an actor."

As a result, Williams, in his first serious acting role since he studied at Juilliard, has been stripped of nearly all the innovative comic maneuvers he's used so brilliantly in nightclubs, on TV's "Mork and Mindy" and in the film "Popeye." Certainly his portrayal of Garp will surprise many of his comedy fans and perhaps disappoint a few. That he was chosen for the role at all may prove to be the film's biggest controversy.

But according to "Garp's" other principals, George Roy Hill's gamble was pure genius.

John Lithgow, who plays Garp's brawny but compassionate transsexual buddy Roberta, had racked his brains for months as to who could do Garp. "Then when they announced Robin Williams," he said, "I thought, 'What a fantastic idea.' Like Garp, he has a kind of earnestness about him, an off-the-wall sense of humor and an underlying sense of sadness. I can't think of any actor who might duplicate that."

From Glenn Close, who plays Jenny Fields, Garp's free-thinking mother: "He's one of the smartest people I've ever met, and it was amazing to watch him and George work out. Robin brings out that wonderful warmth of Garp. Someone described Garp as a mother man, or man mother, and I think it's a great description."

Screenplay writer Steve Tesich agreed. "He's the only person who could do this role," he said. "There's an openness to him, an accessibility that you just don't find in actors anymore. He can do the hardest thing of all--portray a human being and not an exaggerated caricature of a human being."

All of which suggests that perhaps Williams wasn't necessarily acting at all, not in the conventional sense, that Warner Bros. is presenting for our inspection and approval not only Garp but, for the first time, the real Robin Williams. Is in fact Robin Williams, to put it in movie promo terms, Garp?

Williams: "I knew it was in there, I just had to dig it up," he explained, "tap into those things I'd kind of put away during the last four years of doing television.

"There's a side," he said, "that like Garp is very sensitive, painfully aware of things, painfully aware of injustice and pain. It's a sensitivity. Sometimes I'm bordering on hypersensitive. I can cover it up by making fun of it and laughing about it, I can chuck it off, but deep inside I'm going, 'Oh God!'

"It scares me sometimes, the state of things in the world right now . . . My ultimate fear is the annihilation of nuclear war. I mean, that's the real undertoad."

Undertoad is John Irving's code word for the forces of doom and mortality that stock the book and the film, erupting at times in terrible acts of violence, cruelty, weakness and sexual abuse. Garp's is one hell of a life, and still, on his own terms and sometimes by mistake, he lives it heroically, observing it, even writing about it, with compassion and comic wisdom. How should Williams portray this in a man who is, as he put it, "more a reactor to things than an actor?" Williams said he got a lot of advice on this point from George Roy Hill.

"A lot of times George said, 'Listen, if you're gonna do this, you're gonna have to accept the fact that you have a presence and not try and do something just because you're on film.' He put me at ease at one point: He said, 'Just know that when you're on camera, you don't have to worry. If you're thinking thoughts, it will register them.' "

Williams also received help from Irving, who was often on the set, underlining passages of his book. "He would come up and say, 'Read this passage,' " Williams recalled. "Especially in the last scene, the death scene, he underlined the whole passage, of what Garp's whole attitude is while he's dying. And it's helped incredibly, the book was very specific. That's why at the end, hopefully, even though it is death or whatever, he still has a positive momentum to his life. He's still, you know, 'I'm flying, I'm flying.' That's the whole thing about flying versus the undertoad."

Weren't there similarities between Garp and Mork? Both were observers of human life on earth. Both were unrestricted by the narrow posturing of machismo.

But Williams wasn't buying it. Garp was much more a participant in life than Mork, he said. And Mork was basically asexual. He politely mulled the idea over for a few moments, then finally concluded, "I guess the reason I'm having a hard time putting it together is I never in any of my wildest dreams associated the two. It would be like saying, 'Compare and contrast Mickey Mouse and Moby Dick.' "

Then the "Garp and Mindy" subtitle has to go?

Williams laughed, going into a network promo.

ANNOUNCER: "Garp and Mindy," a new series on ABC.

REPORTER: Mr. Williams, will you be going back to TV?

MR. WILLIAMS: (with contempt) No.

TV EXEC: A million dollars?

MR. WILLIAMS: "Garp and Mindy," you got it. Where do I sign? Okay.

REPORTER: Will there be Garp toys? Toys that go "yibit, yibit"?

GARP DOLL: (parrot voice) Squawk! My name is Garp! Squawk!

ANNOUNCER: The Ellen James doll!

ELLEN JAMES DOLL: (tonguelessly) Errrghiiirrraaarrrgh!

KIDDIE SHOW THEME SONG: (skipping along) Garp and Mindy, Garp and Mindy.

GARP AS KIDDIE SHOW STAR: (breathy) Gosh, Min. Roberta's here.

Now Williams was on a roll. He said the film affected him in a very personal way. "I guess it just opened up old heart valves again--I want to have a child so bad right now, it's incredible." When might that happen? "Gonna make the big push this summer," he said.

WILLIAMS: (meekly) I'd like to make another withdrawal from the sperm bank, please?

CLERK: Mr. Williams, you're overdrawn. Sorry, we have to check your account.

WILLIAMS: How far down is it?

CLERK: Er, about 40 quarts.

As for his professional future, Williams said he'd like to make a movie that was a "full-out farce, just 'kick out the jams . . . ,' like what Jonathan Winters got to do in 'Mad Mad Mad World.' To be with a whole ensemble of mad people and just say, 'What do we do today?' "

" 'Cause I have so many wonderful, crazy friends I've met over the years," said Williams. "I'd like to get us all together and just say . . . ."

Now that "Garp," is finished, will Robin Williams return to the favorite normal, healthy, two-sided idiot-savant?

DANGEROUSLY INSANE INMATE: (grinning, drooling, giggling, snickering) . . . Mr. Spielberg, c'mere.