Margot Kidder wasn't giving autographs at last night's Wolf Trap Gala, but her young daughter had yet to perfect the proper celebrity demeanor.

"I never go to things like this," said 10-year-old Maggie McGuane, who wore a dazzled grin and carried a camera. "Premieres, but nothing big."

This particular big thing was a fund-raising celebration of the performing arts farm's 15th anniversary and the upcoming 90th birthday of founder Catherine Shouse. While the hoi polloi filed by, bearing lawn chairs and peering past tall hedges at a tuxedoed receiving line, about 600 monied guests socialized and ate dinner with Kidder, singer Peter Allen, opera stars Roberta Peters and Robert Merrill, jazz great Dizzy Gillespie and Wolf Trap Vice Chairman Beverly Sills. Later all watched Henry Mancini and Liza Minnelli perform.

"There's a certain aura to it," said Merrill of the Wolf Trap Filene Center, where he has performed many times. "It's sort of relaxed, and the acoustics are marvelous. The old wood had a very resounding quality, like an old Stradivarius."

Much of the old wood was destroyed in the 1982 Filene Center fire. But, Merrill said, "They seem to have re-created it."

After informing Merrill he was about to fall victim to a mosquito, Allen said he had come largely to watch his former wife perform.

"I haven't seen her work for a long time," he said of Minnelli.

People like Allen serve as something approaching human party favors at events like this. For $10,000, the most generous donors got a whole dinner table to fill with their friends and were guaranteed the presence of a performing artist. A minor industry exists to supply stars at charity events. Allen, Kidder and Merrill were provided through the efforts of Schecter-Cone Communications, a Los Angeles-New York PR firm. Schecter-Cone booked the celebrity guests at last week's Cancer Ball, and with Cancer Ball chairman Alan Kay serving as cochairman for the Wolf Trap Gala, Schecter-Cone got involved too.

"She's not really sure why she's here, but she's happy to do it," said Mike McAdams, a friend of Kidder's. "She's always been interested in the arts and in government support for the arts."

Allen remembered playing at Wolf Trap during a rainy evening when the lawn seats lost their charm and patrons ran for the shed. "Everyone had to sit on everyone's laps. The audience was incredible."

The dinner was expected to gross about $290,000. At the dinner, Shouse was surprised by a birthday cake and at the performance by a video tribute in which President Reagan, Caspar Weinberger and Melvin Laird wished her happy birthday and one friend offered the opinion that "Kay is not mortal and she is not going to go."

"She gets things done," Peters said of Shouse. "She knows the right people to ask."

"She's even involved in repertoire," said Merrill. " 'What are you going to sing?' she would ask me. She knows her public."

"And she speaks up," said Peters.

"The main thing is," said Merrill, "she has pride, pride in her place. This is her baby. That's what's keeping her young."

Shouse, speaking up later, said, "It isn't my baby. It expresses my wishes, but it isn't my baby.

"This used to be my farm, you know," she said. "I love being over here still. A lot of these trees I planted myself -- it's a very intimate feeling."