It was an evening of good news and great music Saturday at the Kennedy Center Concert Hall. The good news was the surprise intermission announcement that funding has been found for the National Symphony Orchestra's European tour planned for February 1982. The great music came from what is undisputably one of the finest orchestras in this country, now closing its golden anniversary season with a Beethoven feast.

Under the direction of Mstislav Rostropovich, the program included Beethoven's "Leonore" Overture No. 2, the Symphony No. 5 in C Minor and the Piano Concerto No. 2 in B-Flat Major. In the concerto, the soloist was Andre'-Michel Schub, recent laureate of the Van Cliburn International Piano Competition, making his NSO debut. It is easy to understand why this young man is a winner.

Advance reports of Schub's cold perfectionism were only half correct. His playing was in fact note-perfect, but it also was a display of intensity and passion thinly veiled by elegance and charm. The concerto is Beethoven's earliest published orchestral score, and it is proof that the great composer could not merely copy Mozart even when this was what he wished. In it there remains a constant tension between classical form and the romantic revolution it presages. Rostropovich and Schub found and exposed the heart of this tension.

An aristocratic orchestral opening was all but forgotten as the piano engulfed the main themes with articulate fervor. The delicate embroidery of the adagio, which often sounds forced, seemed natural as the intricacies of its beauty were revealed in Schub's hands. And the final rondo, with Rostropovich's brilliantly flexible tempos and faster-than-expected opening, brought a thrilling dialogue of soloist and orchestra.

With the Fifth Symphony, Rostropovich was a master of romantic interpretation. In music as in love, longing can be almost as satisfying as fulfillment, and the maestro proved this with both ardor and patience. The expectancy of the famous E-flat beat in the second bar was held back just long enough, the surprise of the C-major fanfares was simply overwhelming. There was youthful idealism in the opening, and the andante brought patient layers of rainbows from the strings as well as sensuous whispers in the fugato passages from the clarinet, flute and oboe. The terse pizzicato in the third movement led to the simmering drum and to the volcanic rush of the final pages. Previous doubts of the wisdom of a Beethoven festival were banished. With performances such as this, Rostropovich and the NSO should play anything they wish.