The most gripping of many powerful moments on tonight's broadcast of the epic Shostakovich Fifth Symphony from Wolf Trap comes not in the performance -- fine as it is -- but in an interview with conductor Mstislav Rostropovich. He talks passionately about his 30-year relationship with the composer. Finally he comes to the farewell between Shostakovich, the lifelong victim of the party bureaucrats, and himself, in effect expelled from his own country:

"Galina his wife, soprano Galina Vishnevskaya and I had to break it to Shostakovich that we were going to the West for two years -- that was the original plan. We were weeping as we explained to him that we were no longer able to work as artists in the Soviet Union, and that another reason why we wanted to go to the West was so that we could make his works known to the entire world. His parting words were, 'Whose arms shall I die in now?' We left the Soviet Union on May 26, 1974. Shostakovich died on August 9, 1975."

Tonight's performance of the Fifth, taped during a recent National Symphony concert at Wolf Trap, is being broadcast in observance of Shostakovich's birthday. He would have been 79 today.

The Shostakovich Fifth is the single work with which Rostropovich has been most closely identified during his years as the National Symphony's music director. Now comes a television version (at 8 p.m. on Channel 26 and Maryland Public Television stations; simulcast on WETA-FM, 91).

The drama of this program is also in the symbolism for Soviet artists that the Shostakovich Fifth has taken on in the years since its premiere in 1937. In previous years, the musical audacities of the Fourth Symphony and the opera "Lady Macbeth at Mtsensk" had drawn the ire of Stalin, who was determined to force Shostakovich to heel. The premiere of the Fifth would be the test. "Friends say the ovation went on for almost an hour," says Rostropovich. "Above all, it was coming from the musicians. They were happy that his genius was still alive . . ."

The important point is that this symphony is as much an epic of the soul as it is of a troubled society. Unlike some of the later, and longer, wartime symphonies, it is not descriptive in any programmatic way. In those, Shostakovich was working in temporary alliance with the establishment. In the Fifth he was treading the narrow line between truth to his subject and overt defiance of the kind that would be counterproductive.

It all comes to a climax in the hushed, reverent but ecstatic slow movement, which Rostropovich calls the Fifth's "epicenter." "Here you see how big his heart was . . . how his heart suffers. It is something very deep . . . very tragic. I see his face when I conduct it. I see his eyes."

There is no such thing as a definitive interpretation of the Fifth. It is too well known and lends itself to too many different perspectives. Rostropovich eschews the broad rhetoric of, say, a Bernstein. He adheres rather closely to the markings of the score, resulting in a certain severity -- not entirely at odds with the composer's purposes.

What one cannot entirely perceive from exposure to just a single performance is the unremitting intensity with which the conductor always addresses this landmark expression of a central concern of his life and his times. It is a quality that typifies Rostropovich as a conductor, and as a man.