For the third encore on the National Symphony Orchestra's debut here tonight, Mstislav Rostropovich picked a popular song called "Berliner Luft" -- "Berlin Air." Barely had Rostropovich begun the familiar melody before the audience crowding the Berlin Philharmonie began to clap in rhythm. They kept it up through three verses, and when it was over the National Symphony and its conductor owned the hearts of the audience.

"Berliner Luft is tonight Rostropovich Luft," West Berlin Mayor Richard Weizsa cker told the black-tie crowd of more than 200 social and political elite who gathered for a post-concert reception at the Philharmonie. Replied the maestro, "Berlin air is good for my health. I am happy to bring the orchestra from the capital of the United States to Berlin, which is more and more a symbol of freedom to the world." The gathering was hosted by NSO President Leonard Silverstein and the Amway Corp., which is underwriting the greater part of the tour.

For Rostropovich, it was a return, not an introduction. He has appeared in the concert hall as a soloist with the Berlin Philharmonic, and has recorded with them both as cellist and a conductor.

The great concert hall is the home of the Berlin Philharmonic, and its renowned conductor Herbert von Karajan, and no one plays Beethoven in that hall without opening up comparisons with some great performances. The National Symphony and Rostropovich played Beethoven's Eighth Symphony in a way that would make any orchestra proud.

The hall, which was built according to Karajan's specific instruction, is a revelation. It is an eight-sided structure, completely asymmetrical, with no matching plane surfaces and no level flooring. The audience seating surrounds the stage where the orchestra sits. And the result is a triumph of unique clarity, immediacy and warmth of tone.

The Beethoven, however, was surpassed by a titanic performance of the Fifth Symphony by Shostakovich, in that it was musically and emotionally unparalleled. No wonder the audience demanded encores. The National Symphony was heard with a clarity that is never present to its Washington audiences. Its soloists touched special heights in an evening that will always stand out in the orchestra's history.

The Shostakovich closed the concert tonight as it had in Zurich last Thursday night. But unlike the Zurich concert, also triumphant, it did not end with timpanist Fred Begun's stick breaking in two in the last, explosive measure. Begun still received a special ovation when Rostropovich had him stand for a solo bow.