Beneath a dusky sky and a canopy of trees, as an anxious crowd gathered across the street at the Corcoran Gallery of Art, and while lenders of the "Rodin Rediscovered" exhibit at the National Gallery prepared for a formal, IBM-sponsored dinner at the East Wing, Joseph and Olga Hirshhorn sat on the grass with other members of the Corcoran's Affordable Art Sale Committee, enjoying a picnic.

"We didn't get a permit, but we figured we'd be through eating before we were asked to leave," Olga Hirshhorn said.

And later, leaving the park, where the group had sat on blankets in their summer suits, dresses and strings of pearls, one admirer said: "I think it's the Hirshhorns. They set such a wonderful tone."

What they had set, besides impromptu spreads of fried chicken, fresh fruit, and wine on the lawn, was a highly successful auction to benefit the Corcoran School of Art. "The Corcoran school needs $50,000," said Olga Hirshhorn, chairman of the Affordable Art Sale Committee, before the sale began.

So with help from Joan Ogden, vice chairman of the committee, and donations from art patrons and artists, Hirshhorn collected 216 pieces of art in the space of a month to raise funds for the school. Meanwhile, they sold about 1,300 tickets to be the fund-raiser at $5 each. Even before the live auction began last night, at least $20,000 had been raised in bids in a two-day, silent auction, Olga Hirshhorn said at the picnic.

"Tuition only pays for 65 cents out of every dollar," Corcoran director Peter Marzio explained. "So we must somehow raise the other 35 cents." The Corcoran is also receiving a $100,000 matching grant from the Morris and Gwendolyn Cafritz Foundation, according to Marzio.

"A lot of young collectors are very interested" in investing in art at reasonable prices, Jean Nowak said. "They know they are good pieces if the Hirshhorns chose them," she said.

Before the live auction began ticket holders were able to preview the art in the only air-conditioned room of the gallery, and the young faces confirmed Nowak's theory.

"She'd like to decorate and I'd like to invest," said Todd Sampert, 31, who came with his wife, Maureen.

"We came for three reasons," said 30-year-old Christopher Addison, who with his partner, Sylvia Ripley, is opening a gallery of his own in Washington. "To get an idea of what people are buying. To buy what we like. And to support what seems to be a good proposition in Washington that supports all of us."

Finally, the auction began, with more than 500 people packed into one of the non-air-conditioned galleries. Participants cooled themselves by furiously waving their numbered fans, the instruments of bidding. The Hirshhorns were auctioneers, with Marzio overseeing, the sweat dripping down his face.

The auction continued until nearly midnight and raised $48,750. Some of the items went for less than $200, including Steven Kruvant's acrylic "#12," which sold for $125. The highest price, $3,600, went for a pastel by Jean Paul Riopelle that was donated by Mrs. Pierre Matisse of New York. The total raised from ticket sales and the two auctions exceeded the $50,000 goal by at least $20,000.

But even before that was known, Olga Hirshhorn hinted at yet another fund-raiser. Asked whether she would plan an auction in the next year or two, she said, "Ssh! Don't tell my husband."