Half of the National Symphony Orchestra was sitting in the audience last night at the Kennedy Center to hear Shostakovich's 14th Symphony. This work, which the NSO was playing for the first time, uses only about one-quarter of the orchestra, and members who have the week off seemed as curious about it as the rest of the audience.

The verdict was mixed, as it often is on the first encounter with an unconventional masterpiece. "That's about as much fun as a double hernia," one orchestra member was heard muttering as he hurried backstage afterward. It was not an isolated opinion, and it was not really inaccurate.

Fun is not what the 14th is about. After he got this music out of his system, Shostakovich was able to have fun in his 15th Symphony, more than any other work of his mature years. But first, he had to wrestle with the facts of life and death in the Soviet Union, and that's what he did in the 13th and 14th symphonies. You can call them brilliant, compelling, powerful, but you can't call them fun.

"I am a prisoner now," sings the bass in a key song of this symphony, which is really a song cycle for soprano, bass and small orchestra. "Hope ends here. Like a caged bear, I pace back and forth. And the sky--it is better not to see, for it can give me no happiness." The music is slow, gloomy, exactly right. Elsewhere it is tense, sardonic, wistful, haunted with overwhelming fears, but grim resignation is its closest approach to happiness or triumph. Still, its brilliantly spare writing for voices, strings and percussion generates a unique color and vitality. A good performance of it is a cleansing experience, like a well-done Greek tragedy, and it received a mesmerizing performance last night.

This music has been a specialty of Mstislav Rostropovich and Galina Vishnevskaya for a long time; it was composed for her voice, and together they made what may be the definitive recording of it. For this performance, they were joined by bass Stafford Dean, who proved a musician fully worthy of his partners. Members of the NSO string and percussion sections rose to the occasion with playing of tremendous precision and vitality. Although it was the NSO premiere of the work, this was not the Washington premiere--that was given last year by a visiting chamber orchestra from Canada. But even for those who heard that performance, last night must have been like experiencing the music for the first time.

Rostropovich's direction, as much as Shostakovich's writing, made Vishnevskaya the mainspring of the performance. For the first minute or two of her opening song, her voice had not quite reached its full power or perfect focus, and once or twice its sound was submerged in that of the orchestra. But this imbalance passed very quickly. In her second solo (the haunting "Three lilies lie on my unmarked grave"), her voice rang out with splendid tone and the dramatic power of a born actress emerged, not only in the shaping of the words but in gestures and facial expression. The whole work's pathos was condensed into that voice, sweet and strong and deeply expressive, alone in the vast concert hall with only John Martin's beautifully played solo cello for accompaniment, singing of loneliness, suffering and death. It was a moment never to be forgotten, and it was followed by many others equally memorable.

Dean achieved a comparable depth and power, with a voice as rich as the orchestra's low strings, total clarity of diction and superbly calibrated emotional nuances. The strings played superbly and the percussion section contributed greatly to the work's enormous range of colors. It was as fine a performance as Rostropovich has given since becoming the orchestra's music director.

The same cannot be said of Tchaikovsky's "Souvenir de Florence" (originally composed for string sextet), which opened the program. The music is rather uneven, with some passages of great beauty but a rather loose structure that was not tightened in this interpretation. Some of the tempos chosen were very fast and the ensemble playing was sometimes very good but sometimes haphazard. The evening opened with Bach's "Air" from the Third Suite for Orchestra, added at the last minute as a tribute to the late Sir William Walton, whose last orchestral work was composed for the NSO.