Dustin Hoffman is a perfectionist, so obsessed with getting things right that when he did "Tootsie" he wore a fake fanny and false teeth to make him look just like a woman.

He works and researches and agonizes every role, whether it's a prisoner on Devil's Island ("Papillon"), a New York street hustler ("Midnight Cowboy") or a hot-shot reporter ("All the President's Men"). But for "Rain Man," in which he plays autistic savant Raymond Babbitt - a man who cannot connect to the real world, yet who has a special genius for numbers - Hoffman just couldn't get inside Raymond's head. Raymond is a character who babbles on and on in a stream-of-conscience style, nearly oblivious to those around him."I was doing very bad work. It was the worst work I'd ever done," mumbles the Oscar-winning actor.

"I wanted to quit the picture. The only reason I didn't," he adds, brightening for just a second, "is the fact that I'd never work again."

He wasn't kidding. The 51-year-old Hoffman had spent a couple of years trying to get "Rain Man" to the screen. It was widely perceived that without his support there wouldn't have been a "Rain Man." To have him drop out would have signaled a grave defeat.

"All I knew is I was in a terrible world of despair," continues Hoffman, throwing up his hands. "It was not pleasant. I had worked so hard in research. I had all this mountain of information I had worked with." He had read about autism and savants, talked to doctors, spent time with autistic people and their families. In fact, he feels now that he may simply have gone into information overload.

Part of the problem with the role is what had attracted Hoffman to it in the first place: "It was fresh to me."

Autism is relatively unknown. People who have the illness do not look retarded. But they cannot connect with other people . . . not even looking someone in the eye. If someone tries to touch them, even their parents, they pull away. Yet 10 percent have astonishing mental abilities in a single area. For Raymond Babbitt, it's numbers. He can figure a complex multiplication problem in seconds, have the batting averages of obscure baseball players at his fingertips, know by glancing at a spilled box of toothpicks the number that had dropped to the floor.

"I remember that when I met Steven Spielberg I said to him, this to me is at least as interesting as E.T.," says Hoffman. "When you can drop toothpicks and they can tell you the number that fell, this guy is from another planet. And yet he is guileless, a true innocent.

"But for the first three or four weeks of shooting I just wanted to die. I wasn't relaxed on screen. I was self-conscious and it was tying me up and it wasn't spontaneous."

Director Barry Levinson says Hoffman's woes were the result of the role violating all the rules of acting. "The whole thing about acting is interacting," says Levinson. "But in the entire movie Raymond never carries on a conversation.

"In the beginning, Dustin would start doing a scene and all of a sudden he got lost. He didn't know where he was in the scene. He drifted off."

Things got so bad that Levinson and Hoffman were reshooting scenes as they went along. Eventually they redid several early key scenes after the rest of the film had been completed.

Hoffman recalls the breakthrough moment when he finally felt he had reached the soul of Raymond Babbitt.

It was a humid, 110-degree day along a road in suburban Cincinnati where the crew was reshooting a scene that had gone badly the day before. Hoffman's long-lost brother is trying to cheat him out of half of a $3-million inheritance, and Hoffman, in his confused state, is babbling on about buying boxer shorts at a certain K-Mart store.

The previous day they had worked through the script. But on this day they improvised. Suddenly, on the second take, it clicked for Hoffman. Levinson realized it immediately. When Hoffman looked at the video playback, he realized it, too.

"I think the heat and humidity had just broken me down. And then I suddenly realized the obsession of the character (his fondness for minor details). I'm comfortable with obsession. I know what obsession is. I like obsession," Hoffman says with a quirky little grin.

"I could connect with him through obsession. Once we hit that underwear scene I didn't think about autism anymore. I just got obsessed in what that character was into at that moment. That's all he's in."

Distributed by Scripps Howard News Service