The National Symphony's audience did two things Thursday night that seldom if ever had been done before in the Kennedy Center Concert Hall. First, the audience gave a five-minute standing ovation to the premiere of a new composition. Then a fairly large number of patrons walked out on a magnificent performance of the "Nutcracker" Suite.

The NSO audience has not gone crazy for modernism, though you might have thought so earlier, listening to the unrestrained applause for the NSO's first performance of the brilliant, classic Toccata for Percussion by Carlos Chavez. The work that got the standing ovation, David Ott's Concerto for Two Cellos and Orchestra, is a totally beguiling piece of music. And the "Nutcracker" Suite, however brilliantly performed, did not begin until 10:35 and did not end until after 11. Mstislav Rostropovich was almost generous to a fault in picking a program for the orchestral soloists' night, which is rapidly becoming one of the best-loved NSO traditions.

It was a night for the orchestra to display the solo abilities of some of its members, and it did so proudly, lavishly. The evening opened and closed with works that are not called concertos for orchestra but were effectively and quite properly treated as such: William Boyce's gallant little Symphony No. 5 in D, resplendent with trumpets and drums, for a baroque-flavored opener, and the "Nutcracker" Suite for a conclusion with many delicate flavors.

In between, violist Richard Parnas soloed eloquently in Bloch's soulful "Suite hebraique," David Bragunier played the Horn Concerto No. 1 of Richard Strauss (lowered an octave) on a mellow-sounding tuba, six percussionists gave a brilliantly coordinated performance of the Chavez Toccata, and Steven A. Honigberg and David Teie triumphantly introduced the Ott concerto to the world. It was an evening to be long remembered, although (perhaps because) none of the 10 featured soloists was an international celebrity.

The six soloists in the Chavez were F. Anthony Ames, Fred Begun, Kenneth Harbison and Charles Wilkinson of the orchestra, and Albert Merz and Thomas Jones, who play frequently with the NSO. Their performance was calculated to demonstrate that percussion music can be chamber music, with a sense of dialogue and delicate shadings of texture as well as rhythmic vitality. This work, premiered 35 years ago, would have been the climax of almost any concert. It is one of the masterpieces of the 20th century; it sounded that way Thursday night, and it should not take so long before the NSO programs it a second time.

But the real discovery of the evening was Ott. His concerto is dramatic; it sings; it has a sense of dialogue, brilliant display, pensive musings, rich harmonies. It is a superb piece of music and, like the whole program, it received a very special performance under Rostropovich's baton.