There are two possible reasons why the audience applauded three-quarters of the way through Tchaikovsky's Sixth ("Pathe'tique") Symphony last night at the Kennedy Center. Some patrons may have thought the symphony ended with its third movement. Or perhaps Rafael Fru hbeck de Burgos and the Philadelphia Orchestra played so well the audience could not restrain its enthusiasm until the end.

The second explanation is more probable. The Philadelphia's audience in Washington includes some of the most discriminating music-lovers in town -- people who are sophisticated to the point of being blase'. They know the Tchaikovsky symphonies well enough to be aware that the "Pathe'tique's" third movement sounds like a grand finale and its fourth movement does not, ending the music, as it began, with a barely audible whisper. "I applauded because it was so beautiful," one audience member said on her way out.

Still, the program was close to a pops evening. The Tchaikovsky was preceded by Rachmaninoff's Rhapsody on a Theme of Paganini with Earl Wild as piano soloist. And if William Schuman's "New England Triptych," which opened the program, is not in the classical top 40, the reason may be that it is not yet familiar enough. Its melodies (borrowed from William Billings, the composer laureate of the Revolutionary War) are catchy; its orchestration is bright and vigorous, and its moods are splendidly contrasted. To know it is to love it, and the audience loved it last night.

Fru hbeck did not pause to savor the applause at the end of Tchaikovsky's brilliant third-movement march. He plunged immediately into the finale, and when it came to its whispered conclusion, he froze in his final position, silently maintaining the music's tension and holding back the applause for what seemed an eternity. In effect, he was conducting the audience, delaying the cue for its participation in the event. And when he finally gave that cue, relaxing with his arms by his sides, the applause was thunderous, building rapidly to a standing ovation. Still, a part of the audience got up to leave as soon as the applause began. Sophisticates in the Philadelphia Orchestra audiences are like that; they enjoy the music, but when it is over they think about the parking congestion downstairs, where all the spaces were filled shortly after 7 last night. Maybe they applauded at the end of the third movement because they knew they would be in a hurry later.

But most stayed for the standing ovation, which the orchestra had richly earned. It was in top form throughout the evening, and Fru hbeck conducted it with perfect control, fine subtleties of phrasing and dynamics and his usual impeccable sense of form and pace. Earl Wild, in the Rachmaninoff, was a fully equal partner to the great orchestra. It was an exhilarating evening in which ultrafamiliar music sounded fresh and new.