"I'm Shirley MacLaine, and I danced on this stage, believe it or not," said the actress to a packed house at the Washington Ballet's Golden Gala in Lisner Auditorium last night. "I was a student of Mary Day for 10 years. She is totally responsible for the success I enjoy in so many ways today." MacLaine paused. "Because at the end of 10 years she came to me and said 'Shirley, forget about ballet.' "

The audience giggled, and with that MacLaine kicked off perhaps the Washington Ballet's most attended performance. Arts luminaries, well-to-do society patrons and a host of others packed Lisner at as much as $200 a head for the Washington Ballet benefit.

The rewards were not catching a glimpse of Reagan or one of the administration's big three or some visiting head of state. The reward was to see Mikhail Baryshnikov leap across stage in a new work choreographed by the Washington Ballet's wunderkind Choo San Goh. It was also a chance to see Amanda McKerrow, who won a gold medal in the Soviet Union, dance, and to listen to Shirley MacLaine banter in praise of the Washington Ballet and its artistic director, Mary Day. (She made one flub -- she called Amanda McKerrow, McEnroe.)

"Baryshnikov! You only see that once in your life, right?" said real estate man Joseph Schuble. "As Peter Gilsey a member of the board of the ballet said to me, 'Even Pat Hayes would be jealous of me.' "

At the Sheraton Washington Hotel afterward all of those people had dinner. There were two parties -- one in the ballroom where guests ate on mirrored tables, the men in black ties, the women in lots of taffeta. The other party was for the dancers in the Delaware Suite, one escalator ride down from the ballroom. There, Amanda McKerrow sat eating a container of black cherry yogurt while other dancers filled plates from the buffet. Nearby Choo San Goh received congratulations. At another table Mikhail Baryshnikov chatted with American Ballet Theatre friends.

Asked by a reporter how he thought he did, Baryshnikov smiled nervously and looked around as if searching for an exit. "You decide," he said.

"I know the decor isn't much," said the ballet's managing director, Alton Miller, to the small group, "but you're eating and they ain't," referring to those upstairs, who were still on the bread-and-butter course.

"And you're much prettier," said Victor Shargai, a member of the ballet board, to the dancers. A chorus of yeas and applause went through the room.