If Mstislav Rostropivich had been holding a football when he took his pre-intermission bows at the Kennedy Center last night, he probably would have spiked it. Instead, he shook his fist in a victory salute. He and the National Symphony had just played Beethoven and had scored, at least as far as the audience was concerned.

Actually, the Seventh Symphony took it lumps in this performance. It was played with an agressive heaviness, and the outlines of the rhythmic structure seemed out of all proportion to the other elements of the music. The brasses had moments of real vulgarity and one listened in vain for snatches of the dance-like character that helps make this such an appealing movement.

Sensitively played a second and third movements led to a crashing finale that had drive and a reckless excitement but no room for subtlety.

Pianist Rudolf Serkin's appearance signaled a return to clarity and moderation. He attacked the Beethoven "Emperor" concerto with marvelous authority and spun out a performance that had both intellectual integrity and emotional conviction. The Adagio, in particular, was a model of concentration and power, exerted through force. Reflecting this, the orchestra found itself engaged in an almost intimate form of ensemble and the result was more effective than the loudest climax of the symphony.