What is Sandy Duncan doing out of a wheat field?

Peter Pan, for one thing.

"It's one of the few musical comedy books of which you're not embarrassed when the songs start," the singer-dancer says of J. M. Barrie's fantasy which opens at the Kennedy Center Opera House tonight for three weeks. Duncan believes Washingtonians will especially appreciate the show: "I think they deal highly in fantasy here."

Duncan giggles merrily. Snugly outfitted in jeans and a patterned red blouse, her light brown hair neatly cropped, she's clearly in top-flight condition.

At 33, she's long since reconciled herself to the loss of vision in her left eye and to the ups and downs and inbetweens of show business. Still, she regards her impending divorce and career shift from TV to nightclubs and the stage as fresh steps that mark a change in her self-image and ambition.

"I like getting out from under that conditioned response of "I just want to be a homemaker," which is what I told myself for seven years.

"I was really the victim of something. I read "My Mother, My Self." And to finally admit that I'm aggressive - and that that doesn't have to be an unattractive quality - to be at peace with myself, is a tremendous feeling."

Taking charge of her life and career have changed her views about television as well. Duncan won an Emmy for her short-lived series, "Funny Face," but dismissed the idea of another one.

"I don't want one. I could stay out there and continue to do a dippy, vacant person. I made the choice not to.

"Besides, television doesn't treat people kindly, whether you're successful or not. After six years on a show, they'll say, "I don't think he's as good as he used to be."

"The fact is that you're as good as you used to be. They're just tired of you. You have to pull flowers out of your armpits to entertain them. I'm very happy to get away from it for a while."

So even if she's creeping out of Peter Pan's age bracket, she jumped at the offer.

"The summer stock people had asked me what I'd like to do. There are very few musical comedy vehicles for women. The ones that do exist are often kind of sappy.

"We were relegated to shows like "Sweet Charity," which I thought I could do better in five years, or "South Pacific," which had been done to death, or "Peter Pan," which hasn't been done for 25 years as far as national exposure. It also lent itself to adaptation for a dancer. Mary [Martin] was a singer. I'm primarily a dancer."

Duncan had capered about as Peter Pan for five weeks in 1975 in Dallas and on the John Kearnley circuit in the Southwest. "We had several people come to us to bring it to Broadway," she says, "but the rights were tied up."

So, with a Broadway production in Never-Never Land, Duncan turned to a night-club act. Along the way, she discovered Wheat Thins and began making her famous television commercials. She says she hasn't seen them. "I really don't watch television. Not out of snobbery - I just don't have the time." She pauses, "Oh, a little out of snobbery. I don't think it's very good."

People around the country now recognize her because of the commercials, but she's not worried that the frequent airings might obscure her earlier image as a performer.

"You run that risk whenever you do something new," she said, turning serious. "It's amazing to me how short peoples' memories are. The thing that was great about the commercial was that it allowed me to gamble on my nightclub act."

Getting nightclub managers to take the act seriously, she says, was a "crap shoot."

"People in nightclubs are very leery of television people. So many television people have decided that because they have a following, they'll throw a show together and make a mint in Vegas. But they don't have the training or the background to get on a stage and hold an audience for an hour. Nightclub people have been burned."

Duncan believes that nightclub performing is "the hardest work you can do because of the two shows a night, no days off, the hours you have to keep, the conditions you have to work under, and the cigarette smoke."

But "I loved it," she says. "It was the first time in my life that I had any sense of creative control at all."

So there she was earlier this year, in full control, doing her act in Florida when an old friend, producer Zev Bufman, came to see the show.

"Zev said, "My God, I'd forgotten about your singing and dancing. Why don't you do a show for me this summer?"

"So Jack [Duncan's manager] said, "She'd really like to do Peter Pan," and I said, "Don't start that against! We can't get the rights, so just don't start it."

"Anyway, Zev checked into it, and it turned out Michael Bennett had the rights. But he released them. He said, "Fine, if she wants to do it, and you want to do it with her, I'll let you have them." I couldn't be happier."

There was a time when she could have been. Duncan lost the sight in her left eye about four years ago. At the time it seemed that the misfortune would jeopardize her career. Luckily, things never got to that point, but confusion about her medical problems still troubles her.

"I had a brain tumor that pressed on the optic nerve. Over a period of months, it just cut off the blood supply.

"I get so many letters from people who think I have a prosthetic eye. But it is my eye. The press have been incorrect. Like Rona Barrett even as late as three weeks ago. I'm going through a divorce now and she said, "Well, Sandy Duncan, whose husband-doctor performed the operation and fitted her with her prosthetic eye...." First of all, that's wrong. He was not one of the doctors. And secondly, it's not a prosthetic eye."

"She corrected it," Duncan's manager, Jack Malthen, assures her.

She seems more fatalistic than angry. Frowns barely begin to crease her face before they disappear.

Back in November of 1974, when she underwent the operation, her first reactions were "denial and suppression."

"I thought I was going to die. I hadn't come to grips with that trauma until recently. I remember one of the doctors at U.C.L.A. coming to me and saying, "You know, we're amazed by your cheerfulness." That was my way of dealing with it then.

Duncan fixes her eyes on you as she speaks. Her irises are bright blue. No wispy red lines mar the white around them. Only at certain angles does something seem amiss.

"How many things I've lost because of it I have no way of knowing. Like films and stuff. That may enter into it. I don't know."

She shrugs away any serious impact of the operation but acknowledges that it makes a difference.

"There's a certain amount of adjustment obviously for dancing. I was a little fearful of that in the beginning. I really know now that if I reach for something, it's just a couple of inches further than I think it is. Turning's a bit of a problem too because I have no peripheral vision. Turning to the left is hard.

"But," she stresses, "I walk over chairs in my act, I do lifts, and so on. I'm more physical than anyone in the business my age."

Her role in "Peter Pan" should prove it.

"Peter Foy, who flew Mary Martin, is doing the flying. We have a single wire harness that I wear in the first act. In the ship scene, we're using a double somersault harness, which was never used before. I think he just devised it.

"It's very cumbersome. I'm lucky I'm slight because I'd look like a football player out there. You're suspended from two wires which create a balance point. In a single harness you can't do flips because you have to fight just to stay up. But in this you can flip around and spin like a skater and turn upside down and all types of things."

Duncan talks excitedly when she talks about the show, which is headed for the Lunt-Fontaine Theater in New York in August. She loves New York and can't wait to get there. She sounds as though she can't wait a moment to get back on stage.

"I'd love a year run," she says without a hint of self-doubt.

Her manager, perhaps more familiar with the demands of a long Broadway run, sounded a bit dubious.,

"Just make a copy of that tape for me, will ya?" he asked.