For Rich Little, Ronald Reagan is a great opportunity. Also, a small risk.

"He's not easy to do," said the impressionist, who was preparing to unveil his imitation of the new president at last night's inaugural gala. "But the thing is that if it clicks, people will really respond. Right now, nobody knows whether a Reagan impression will work. But I think I've found the key."

Demonstrating, he tilted his head down slightly, and began shifting from one foot to the other like a cowboy at a dinner party. "Well," he exclaimed in a perplexed, aw-shucks monotone, "there he goes again."

It was Reagan, all right.

"It'll be easier when he's in office a while," Little said. "So far, that's the one line people remember from the debates with Carter. I noticed that Reagan has a hesitant kind of voice, a little raspy from age. Also, he begins every sentence with 'well.' A woman who worked for him told me that, and it's true. But what he projects is more an attitude than a visual impression. Kind of a movie image of a cowboy."

Nixon was easier, from the beginning.

Little seems to draw into himself, hunching his shoulders. He looks down his nose and waggles his jowls. "Tell the chef to get moving," he says with eerie familiarity and a groveling smile. "I am not a cook."

"I did my impression for President Nixon, and he had absolutely no reation whatsoever," Little said. "President Ford was terrific, he fell apart laughing. Carter had a sense of humor, too, when I did my Carter for him. He was easy, actually -- the crinkly smile, the accent, the peanuts. A dentist made me some Carter teeth which snapped on over my own, and people loved it."

Rich Little, 42, is the country's best-known impressionist of the moment. He is an unpoliticized entertainer -- "I didn't campaign for anybody" -- with a repertory of 150 personas. Those impressions have kept him steadily on television, at Las Vegas and on tour, and provided him with a house on the beach in Malibu, Calif.

"I don't think of myself as a satirist," he said. "I tell dumb jokes, that's all. I'm not trying to be Mort Sahl or somebody like that."

He demonstrated with a brief exchange between Walter Cronkite and Ronald Reagan. A Groucho joke,' he called it:

Cronkite: "Mr. President, you've said you'll work only nine hours a day in office."

Reagan: "Well, I don't know where you got that. I plan to work 25 hours a day."

Cronkite: "But how?"

Reagan: "Well, I'll get up an hour earlier."

Little says he was booked on the inaugural program without his material being screened. "They didn't have to worry," he said. "Frank Sinatra vouched for me."

According to Little, not every well-known person makes a good subject for mimicry. "I'll tell you who'd be hard," he said. "Robert Redford. Or Rock Hudson or Gene Hackman. There's nothing there to work with, really. They're big, strong guys without any easy mannerisms. And a masculine, deep voice is the hardest one to do."

On the other hand, he learned his Truman Capote imitation in 10 minutes.

Little concedes that the career of the impressionist is not without peril; where are they now, the mimics of only yesterday? Frank Gorshin: "Hasn't been working much. Never did politicians anyhow," Little says. Robert Frye: "Disappeared after a while." Vaughn Meader: "All he had was Kennedy. When Kennedy went, he went."

Things can go wrong, even when the subject is in the audience.

"You know what happens when you do an impression of someone who is sitting in the audience? Just as you begin, everybody looks at him, instead of you. They want to see if he's laughing or not. If he is, everybody laughs with him. If he's not, you're dead."