In the beginning, David Lloyd Kreeger thought it was a lousy idea. "My poor friends and family have had to endure my 50th birthday party, my 55th, 60th, 65th and now my 70th," he said. "Why inflict it on them?"

Enter the music director of the National Symphony Orchestra, also known by many as one of the greatest cellists around.

"Slava Rostropovich is going to play for my birthday party?" said Kreeger. "Well, even I will come."

He did, of course. And so did 450 others to celebrate the 70th year of Washington's resident Renaissance man at the Capital Hilton Saturday night. "A real mob scene," said U.S. Circuit Court of Appeals Judge Harold Leventhal.

But the mob was black tie, glittery, generally well-behaved and, later, hungry. That was the fault of the musicians, who were 40 minutes late and so pushed back the carefully planned schedule of concert, reception and dinner.

At 9:30, guests were still wolfing the stuffed mushrooms resting beneath a fountain that changed color, and S. Dillon Ripley, the secretary of the Smithsonian, was surviving by talking about the spun-sugar cakes he ate as a child.

"You'd have these little nests of sugar and little ice cream balls of hens and chickens sitting in them," he said. "Marvelous."

The birthday party was arranged by seven organizations: the Kennedy Center, the Arena Stage, the Corcoran Gallery of Art, the National Symphony Orchestra, American University, the Washington Opera Society and the Jewish Community Center. Kreeger, the former chairman of GEICO, is also a former chairman, present board member or continuing philanthropist for all seven organizations.

Besides Kreeger, Rostropovich was clearly the star of the evening. "I'm in love with him," said one young woman. "He kissed me and I'm never going to wash."

Earlier, the cellist's other talents had been displayed in a performance including Rachmaninoff and David Popper that brought guests to a standing ovation. "I played with my whole heart," said Rostropovich, who was home with a 102-degree fever the day before. "I played for my friends, and that inspired me very much."

There were several other performances during the evening, but these were of the amateur variety. Livingston Biddle, chairman of the National Endowment for the Arts, sang a croaky "There is Nothing Like Our Dave" to the tune of "There is Nothing Like a Dame," and Kreeger himself played a Mozart Scherzo Duet on one of his two Stradivari violins. The guests loved it.

"I probably should have warned you all," said Kreeger. "Even the slightest applause forces me to play an encore." And he did.

The party crowd was heavy on arts-establishment Washington. It included Corcoran Director Peter Marzio, Kennedy Center Chairman Roger Stevens and American University President Joseph Sisco. There was also a smattering of arts-supporting politicians like Rep. John Brademas (D-Ind.), Sen. Henry M. (Scoop) Jackson (D-Wash.) and Rep. Sidney Yates (D-Ill.). Yates spent the early part of the evening reminiscing about old times on the Hill with former Minnesota senator Eugene McCarthy.

McCarthy, Democrat turned independent who writes poems and runs for president a lot, promised that he may try again this election. He claimed to know Kreeger from events at which he read poetry and Kreeger played Mozart.

Still another "I'm-thinking-about-it" presidential candidate was there, this one in the form of Sen. Larry Pressler (R-S.D.). Presler said he hasn't made up his mind, although he has become a regular on the fall social circuit. "But I was home by 11," he said on a party-hopping last week.

There were few young faces in the generally over-60 crowd. The waiters, a musician or two and a woman who turned out to be the page-turner for the pianist were exceptions. "It's no way to get famous, but I do have a good time," said the page-turner, Jackie Anderson.

Msgr. Joshua Mundell of the Immaculate Conception Church was on hand, too. He identified himself as the pope, two weeks early, and then continued with what appeared to be an impromptu stand-up comedy routine. He claimed that the Kreegers, who are Jewish, "are nice enough to be Catholic."

Also spotted was TV show hostess Deena Clark, who asked White House Curator Clement Conger whether she could sit in his lap at a state dinner this week.

At the end of the party, Kreeger got a ceramic cake, suitable for display but not eating, from the seven organizations. "What a wonderful, glorious evening," he said.

Oh, and one other thing. Kreeger's 70th birthday was actually Jan. 4, which as anybody can tell, was months before Saturday night. But Sept. 15 was the only date the seven organizations could agree upon, and it was either that, or seven different parties.

Which, Kreeger said, "would have been madness."