Composer Leonard Bernstein, whose Mass is playing in the Kennedy Center Opera House for the next two weeks, moved over to the Concert Hall last night to join Mstislav Rostropovich and the National Symphony Orchestra in a special salute to the Kennedy Center's 10th anniversary.

Bernstein, as conductor and pianist, joined members of the orchestra for the Mozart Concerto No. 17 in G, K, 453. The woodwind choir of solo flute and pairs of oboes, bassoons and horns, was seated at the front of the stage on Bernstein's right, an arrangement which provided exquisite balance with the strings, and gave the winds and piano the requisite rapport for the frequent dialogues in which they engage.

It is one of the wonders and at the same time one of the mysteries of'today's musical world that Bernstein, who spent August in seclusion composing an opera, and who carries a heavy conducting schedule, keeps his pianism in brilliant, top form. The delicacy with which he outlined the ravishing melodies of one of Mozart's greatest concertos was matched by the grace, charm and wit with which he filled its pages. His playing can easily stand alongside that of any of today's most noted Mozateans.

There was style and dynamic shading both in his piano and in the crisp response his direction elicited from the orchestral musicians. The articulation was as ideal as the lovely sound that pervaded the entire concerto. His presence in both Opera House and Concert Hall the past few days has given Kennedy Center audiences another opportunity to cheer this man who has contributed so much to this cities musical enrichment over the years. Last night's standing-room-only audience stood and shouted its appreciation.

After intermission, Rostropovich came on stage to lead the Second Symphony of Brahms. The orchestra, which formally opens its 51st season tomorrow night, was in excellent form. A detail worthy of mention was the beautiful sound of the chords that closed the first two movements. They had every shade of balanced ensemble and warmth that marks truly outstanding Brahms ensembles.

Rostropovich conducted with great affection, but without letting his devotion interfere with a reading that properly emphasized the kind of motion that gives the relaxed music its finest impulse. Precisely as marked, the first movement was not "too" allegro, nor the succeeding slow movement "too" slow. As in the Mozart the Brahms had a large share of beautiful passages for solo winds. It is appropriate to salute the National Symphony's new first oboe, Rudolf Vrbsky, in his first appearance with the orchestra in the Concert Hall. He has been heard with appreciation in the orchestra's outdoor summer concerts, but the beginning of the third movement showed how welcome his presence wil be in the reason now beginning.

The third movement was also remarkable for the way Rostropovich handled its basic pulse, which remains constant throughout, even while undergoing shifts in tempo. The concert, played as a benefit for the Kennedy Center's specially priced tickets for students, senior citizens, handicapped and enlisted personnel, was both a rare treat and a grand curtain-raiser for tomorrow night's opening.