Reprinted from yesterday's late editions.

he opening concert of the National Symphony Orchestra began Tuesday night with a letter from President Carter and ended with an encore dedicated to the memory of Benjamin Britten. It was an immensely auspicious beginning for the music directorship of Mstislav Rostropovish.

The President's letter welcomed the new conductor and said that while the Carters were unable to be there last night they were looking forward with pleasure to hearing the orchestra under Rostropovich often in the future.

Even before the concert began there were new sounds backstage at the Kennedy Center. The orchestra, at the request of its new director, now does its pre-concert tuning up behind the scenes, and comes onstage all ready to begin playing.

Thus with Rostropovich very much in evidence backstage, the musicians were walking aound bowing, warming up instruments and wearing looks of intense anticipation.

The music began with a stentorian "Star-Spangled banner" in which the audience heartily joined. From then on, it was all a matter of watching Rostropovich take his charges through the paces he has carefully prepared in the last two weeks.

The Oberon Overture of Weber smoothed out quickly after some early sounds of nerves in uneven flutes and some not-so-well dotted notes from the brass choir. But as it proceeded, it grew in strength and style. Rostropovich called for frequent dynamic shadings that are often overlooked, shaping phrases with unceasing care.

The collaboration of Rostropovich, Rudolph Serkin and the orchestra in the Fourth Concerto of Beethoven provided the most satisfying performance of the concert, not only because the music, but because everyone on the stage sounded determined to make every note a thing of special beauty.

Serkin was in tremendous form, playing with a combination of demonic and angelic powers. His tone sang radiantly, his pedaling became a thing full of marvels, and his knowledge of the music gave a major share in the exquisite details that emerged.

Rostropovich supported the pianist at every moment with orchestral playing that was sculpted to match Serkin's phrasing. The approaches to cadences were of singularly poetic expressiveness to which the orchestral musicians gave particular beauty.

The Dvorak Seventh Symphony came off extraordinarily well both in the full ensemble and in the many solos that enrich it. Rostropovich reads it in broadly romantic terms, the only ones appropriate. But he never sacrifices the composer's intent in graceful melodic lines or rhythmic figures to personal feelings.

The encore was the Storm from Britten's opera, "Peter Grimes." It was played with all proper thunder, and, in the tender moments, lyric appeal. The audience, filled to Standing Room, shouted its approval of everything.

Rostropovich played the encore in memory of Britten, to whom he is dedicating this week's concerts. His longtime friend and colleague had begun work on a new major cantata expressly for Rostropovich and the National Symphony. His death last winter ended his work after he had finished 11 pages of the music.

The audience Tuesday night included representatives of the press from New York and the West Coast, as well as leading magazines and wire services. Some of the audience, in their usual rush to the exits, missed out completely on the encore.