When her daughter Alix was born 22 years ago, Iris Mitgang recalls, "I announced that she would be the first woman in the White House."

Now, Alix is a member of the Student Senate at the University of California, Berkeley, from which she is graduating this year. Her mother, who is finishing her second year as chair of the National Women's Political Caucus, sees no reason to retract her original prediction, though she is reluctant to say when it might come true. Alix will be eligible for the presidency in another 13 years, and Iris Mitgang smiles at the suggestion that the country and the candidate may be ready at about the same time.

Women candidates were topic number one last night at Wolf Trap, at least until 8 p.m., when talk gave way to music, in a concert highlighted by the first musical collaboration of two women named Sarah -- Caldwell and Vaughan in alphabetical order.The concert and the gala (though charmingly informal) $150-a-plate buffet dinner was sponsored by the Women's Caucus, which is celebrating its 10th anniversary and its growth from a membership of 271 to more than 55,000.

"Our membership is growing among women in both political parties," said Mitgang, "and as we approach our 10th birthday, our message is being heard. I think the fact that we have Joan Mondale and Barbara Bush among our honorary co-chairs shows that. There are a record number of women in Congress and state legislatures. Only four state senates are still without their first woman member, and we're working on that."

What the caucus was doing about it last night was raising funds and having a good time. The goal of the dinner, concert and afternoon reception at Bloomingdale's was $50,000. Final figures were not yet in, but nobody seemed worried. Iris Mitgang chatted easily with Effi Barry, Joan Mondale and other guests, while Mayor Marion Barry circulated among potential constituents. One of his longest conversations, however, was with an out-of-town vistor, jazz pianist and impresario Billy Taylor, who will be a prominent participant in the Wolf Trap Jazz Festival next weekend. "My brother tells me you're doing a great job," Taylor told Barry, "and I take his word."

Black tie was optional at the dinner, and Barry was one of the few hardy souls who chose that option in the 86-degree heat and high humidity. It may actually have been cooler on the lawn, a few feet away from the buffet tent, where picnickers were able to enjoy the dinner music of a jazz quartet named Sidney but missed the classically simple buffet of high-quality ingredients supplied by the Elegant Gourmet caterers: crab claws, salmon, cold roast beef, ratatouille and broccoli salad. The elegance remained, but not the simplicity, in a desert called "Paris Breast" -- bagel-shaped sweet pastries filled with whipped cream, mocha and kiwi fruit. -

Sarah Caldwell and the National Symphony Orchestra opened the musical program with a crisp, neatly balanced "Marriage of Figaro" Overture and a tempestuous reading of Tchaikovsky's "Romeo and Juliet." After intermission they gracefully took the role of accompanists to Vaughan, who is essentially a one-person show. By the second chorus of "Fascinatin' Rhythm," Caldwell, sitting in her conductor's chair, had begun to develop a little syncopated bounce in her movements. The brass section obviously enjoyed itself tremendously in some numbers, and Caldwell and her combo might be able to get some gigs on the Big Band circuit. But it was really Vaughan's show, from "Embraceable You" to "Send in the Clowns," which she made uniquely her own. Obviously suffering from heat, she was slightly below her best form -- but there is still nothing else quite like her.