Barbara Cook's distinctive and highly personnel act works at the Waaay Off Broadway cabaret and at The Bottom Line in New York; she expects it to work on a program she is planning for Dutch Television and for tentative Berlin and Paris bookings next spring.

Her act worked well enough to get her booked for three shows at the White House, yesterday, but she still wonders whether it can put her in touch with a really large audience.

Cook sums up her stylistic problems with her usual directness: "The record stores don't know which bins to put my records in."

It used to be easier, when she was starring in Broadway musicals: Marian the Librarian in the original production of "The Music Man," Cunegonde for the premiere of Leonard Bernstein's "Candide," and top roles in revivals of "Carousel," "The King and I," "Show Boat" and other shows. The musical comedy is an established pigeonhole with a bin of its own in most record stores, and if it is currently going through a sort of crisis, at least people know what it is.

But that was in the past. What Cook is doing now is harder to define. If she were a foreigner, she could be put in the same bin with Edith Piaf. And if the material she sings had been written by Puccini rather than Americans who range from Cole Porter to Billy Joel, she might find herself sharing a bin with Anna Moffo.

But what she does is sing popular songs with a classical perfection, and it's not easy to find the right pigeon-hole for that kind of work.

It's the latest in a series of careers that began in Atlanta when she was 15 and lied about her age so that she could dance in a chorus line. In the late '60s and early '70s, there was a five-year period when she didn't sing at all in New York and played straight dramatic roles in such plays as "Little Murders," "Any Wednesday" and Gorki's "Enemies."

Her private life has seen as many twists and complications as her professional career-including a divorce in 1965 after 13 years of marriage, the complications of raising a child (her son Adam, who is now 19) while pursuing a career in show business, and above all an illness-hypoglycemia. Her condition went undiagnosed for years because the symptoms of hypoglycemia-drastic weight increase and behavioural changes-are usually given non-medical explanations.

"I was ill for a long time without being aware of it," Cook recalls now. "Once I found that out, about two years ago, my whole life changed. Now, I watch my carbohydrates very carefully, and the nice side-benefit is that you begin to lose weight. I've been losing a lot, and I'm feeling wonderful."

Noticeably lighter than she was a few years ago, Cook is still nowhere near the thin young thing who once danced in Atlanta and sang in "The Music Man" when it was new. She seems to have come to terms with this reality, and her personality off-stage is as sunny and positive as the one she shows her enthusiastic audiences. "I think it's healthier in every way to realize that you can't reach that sylph-like ideal that you see in all the fashion photos. And get off that seesaw, going up and down all the time."

Then, a bit wistfully: "At least, now I know I'm not too fat for the White House."

Intimacy is an important part of the new Babara Cook performing style, which began to emerge in 1973, when she did a summer tour with a Gershwin program in honor of the 75th anniversary of his birth.A little later, she had a gala evening at Carnegie Hall, which was recorded by Columbia Records, and in collaboration with arranger and music director Wally Harper she has tailored a one-woman show that is like a dozen miniature dramatic roles one after another.

"What I did before was a character in a play," according to Cook. "What I do now is all myself-a lot of different facets of myself. The opportunity to be myself on stage is one of the things I enjoy most, but it's also frightening; unlike a dramatic role, you have nothing to hide behind."

The atmosphere of cabaret performing, rather than theatrical work, "is like being at a big party where someone says, "Barbara, won't you sing for us?" You're still performing, but there aren't so may barriers."

That's the feeling that comes across in her performances at the Waaay Off Broadway. There tends to be something like a party feeling there when the audience is relating to a performer it knows and likes-an easy give-and-take across the footlights that can almost develop into a conversation between audience and performer. "I think of myself as being in the communication business, not the music business," says Cook.

What she communicates is songs that are worked up into sort of dramatic monologue-usually romantic songs like "Wait Till You See Him" or the hilarious and touching "Vanilla Ice Cream," which she develops into little studies of human nature. But the climax of her act each evening is a slow performance of "Carolina in the Morning": a tour de force of pure languor which is also a celebration of the pure joy of living. Connecting these songs, each evening, is a monologue that develops into a dialogue with the audience. The basic format in the act remains the same from night to night-circumscribed by the arrangements which have been worked out with her pianist and bass player-but the spoken part changes from one performance to the next, with a few recurring one-liners as landmarks.

"What I'm trying to do it put people in touch with themselves, their emotions, the other people in the room so that all kinds of exchanges can take place," Cook sums it up. "When it works, I think that something special happens."