MARY MARTIN holds up a pillow that will be in a museum some day. On it is a needlepoint sketch she did of Oscar Hammerstein II while he was writing the lyrics for "A Wonderful Guy," which she sang in "South Pacific," one of her innumberale legendary smash hits.

"Oscar usually wrote at a standing desk," Martin says, sitting in the Park Avenue apartment of Hammerstein's producer son William. "But this particular lyric he wrote lying back - see? That's the head, and this is absolutely his body. I have one of Dick Rodgers with his hands on the piano while he was writing the music, too. One Christmas I made one for Oscar, one for Dick, and one for (director) Josh Logan."

She smiles and puts the pillow down. In the supermarket, you might run into this 63-year-old ingenue and think her just any well-off old lady from Palm Springs, until she smiled, or giggled a staccato "Ah-HAH!" or you really got a load of that very deliberately blonde hair. It's not just another person. It's MARY MARTIN.

"A man came out of a crowd once and said to me, 'You are a pillar of the American theater," she laughs. "I said, 'I'm a what?' I thought, 'Well, I am going to have to walk around straight up and down like a pillar."

Now she is coming out of a personal haze - like Dolly Levi did. For the past three years she more or less secluded herself in Palm Springs after the death, in Brazil where they'd spend four years together, of her husband Richard Halliday. She has "remade" her life now, she says, and won't be kept down. She returns to the stage in a two-character Russian comedy, "Do You Turn Somersaults?" by Aleksei Arbuzov and costarring Anthony Quayle. Previews begin Thursday for a six-week run at the Kennedy Center.

She won't tell whether she indeed turns somersaults on stage. "I want it to be a surprise," she says coyly. During a subsequent rehearsal, she tore a cartilage in her right knee but continued on in a cast. She's haltable but unstoppable. "I am sort of accident prone," she notes. "I mean, I've hit all the walls in the United States, and several pits. We'll see."

Martin is still saucy, still cute, still Peter Pan, Nellie Forbush and Maria von Trapp of "The Sound of Music." Her autobiography. "My Heart Belongs," published last year, was one long gush of beneficent reminiscence; everybody was "wonderful," "adorable," "darling" or "blessed." She even referred to Elizabeth II as "that dear sweet queen." And herself as "Texas-corny me."

It might all be a little on the insufferable side, except that, how many Marty Martins do we have? Even if she seems, in Hammerstein's phrase, "a cliche coming true," it's the kind of cliche that gets more cherishable by the minute. There aren't that many pillars of the American theater that are still standing.

If you'll excuse an expression I use, I'm in love, I'm in love, I'm in love. I'm in love with Mary Martin. "I'd said. "No, I don't want to do anything." Martin recalls of her premature retirement to Palm Springs, where she sat around chatting with her "best friend," one-time movie star Janet Gaynor. But her agent kept sending scripts.

"They werwe all 'Life with Father.' Life with Mother' all these things that might makes a wonderful musical some day. Oh, and 'Arsenic and old Lace'; everybody wanted me and Merman to do 'Arsenic and Old Lance' as a musical. Abd. oh. new ones, too. Lots of new ones - actually that one that Liza Minnelli has been doing now called "The Act" was written and brought to me, but . . ." - she makes a tart aside, almost whispering - "I don't think it's going to come into New York," meaning it'll fold on the road.

"And on, lots and lots, and I said, I don't want to do an old play made into a musical and I don't want to do anything I've done before, so I said no to everything, which is not like me." Then she read the Arbuzov play, originally called "Old World," and "I absolutely adored it." After some complicated negotiations, the deal came through.

"It's the story of two people finding each other," Martin explains. "They're people who've led completely different lives and meet and get together and don't get together and you don't know till the very last minute if they will stay together. It's laid in Russia, but in 1968, so it's not a 'Cherry Orhard' or something like that. I really think it could be taking place anywhere in the world - Cape Cod, Boston, Switzerland, anywhere.

"I play a kind of pixieish lady. She's just a little fey but you understand why she is the way she is. The most delightful thing is that I play a woman of approximately my own age and that is something I want to do. I want to play my own age. I want to I'm a very happy person and it can be done if you think as positively as I have always thought and always will. I mean, there are an awful lot of people in my age bracket that this play will help think better."

Is the character much like May Martin?

Giggle, "I think. She talks a lot. I talk a lot. Since I've been off for eight years (since 'I Do, I Do), I've made up for all the lost time when I didn't say anything. I just talktalktalk," Giggle.

There is a little song running through the play, but it is not a musical. "No, I made a decision: I won't do big musicals again, ever. Because I don't want to not do it at the top of my peak, or whatever it is, and there is no way to do eight shows a week and do that. No way."

Still, Martin was coaxed out of silence earlier this year to do a big benefit in New York with Ethel Merman. People who were there say it was a night of nights of nights. Though it's a persistent theatrical rumor that the two despise each other, Martin says there has "never, never" been a feud. The two most illustrious actresses in the American musical theater went on that night and stayed New York.

"They'd been asking me if I would do this for three years, and I hadn't sung for three years - four, five? - nothing, nothing, nothing, so I kept saying, 'No, no, no,' I said, 'Tribute?' It sounds like you're dead! Well one day I answered the phone, like a jerk, and it was this theatrical lawyer who said, 'Ethel Merman says she'll do it if you do,' so I said, 'ALL RIGHT!' 'cause I figured if I didn't say yes I'd never sing again. And I was afraid to sing, I truly was, and I'd never been afraid, so I said 'yes.'"

What a night. "It was like Yankee Stadium, hitting 12 home runs like that (she clicks her fingers several times). I've never heard a sound like that audience. It was like everybody was on springs; they just jumped up, and we hadn't even done anything yet! Ha ha ha HA!

"You know, Ethel - I'm one of her biggest fans. She makes me laugh. She doesn't know she's that funny. She really doesn't. She doesn't have the vaguest idea how FUNNY she is. I just fall off the floor. She just slays me. But it was wonderful, and she was in the best form I have ever heard her. She was absolutely- and there's no question about it - at her peak that night. She'll never hit it again - er, I mean, she may hit it, but, it was the best in the 30 years I've known her."

It's time for rehearsal and Martin decides to wear the white jacket a waiter gave her at a restaurant on a previous night. It was this "darling" little restaurant, she was cold, everybody loved her, and the waiter gave her his jacket, and "I went into the kitchen, kissed the chef, kissed the waiters, kissed everybody . . . " They did everything but sing "Hello, Mary."

She models the coat. "How about that? Isn't it cute?" Then, encountering her hefty chauffeur, she says, "If you're not there when we finish tonight I'm gonna drop dead because I'll be so tired" and he says, "When I'm behind the wheel I make sure I find you, Mary. The other drivers may not be in love with you as much as I am." Mary says, "I know, I know."

She bursts into the rehearsal hall like this: "Good morning, hi there, how is everybody, doodley-doo," and claps her hands. It probably wasn't much of a room until she walked into it. Then a few moments later she demonstrates how she does her voice exercises to a taped piano accompaniment.

Up the scale, and pressing her hands into her sides, she chants, "Zeet zeet zeet zeet zeet zeet zeet . . . isn't it a beautiful day . . . hah hah hah hah zeet zeet zeet zeet" and then she puts her hands on her hips, with her legs apart, and suddenly it's Peter Pan right there in person.

She missed the new version of "Peter Pan," with Mia Farrow, when NBC showed it last year. The original, starring Martin, still exists on videotape. There are no plans to show it. "But it'll be shown again some day," she says with a bubble laugh. "When I pop off, they'll put it on every year like 'The Wizard of Oz,' ahah! I'll be flying in your windows like crazy."

It is awfully hard to imagine this dynamo lounging around Palm Springs. "I do love the life," she says of the theater, and it shows. Told incidently that the Cinegrill, in Hollywood, where she began singing professionally, is still there, Martin pauses slightly for effect, winks, and says smiling, "Sure honey, I am, too."