There was a rememberance of the past and an excitement in the new as the National Symphony Orchestra opened its 50th anniversary season last night.

Mstislav Rostropovich conducted the orchestra in the Kennedy Center Concert Hall in music that was closely associated with the orchestra's early years and then led a flaming performance of the Fifth Symphony of Shostakovich in a manner that proclaimed once again his own dominating command of the podium previously held by Hans Kindler, Howard Mitchell and Antal Dorati.

There were floweres at either side of the stage and a huge sunburst of them in front of the organ pipes above the musicians. When the concert was over, Rostropovich paid touching tribute to Kindler before unveiling the Lindsay Oliver portrait of the NSO founder, which now hangs at the end of the corridor to the right of the Concert Hall. He said, "Always when there is a good thing like the National Symphony, there must be a founder. And now we say a prayer for him who is not now with us but whose spirit still is here." w

The evening was both a beginning and a closing. At the end of the intermission, Board President Austin Kiplinger thanked Robert Isele, who has played trombone in Washington for 40 years -- 24 with the Marine Band and the past 16 with the National Symphony. Kiplinger presented Isele, who is retiring this week, with a plague.

In the first half of the program, after a rousing "Star-Spangled Banner," Rostropovich conducted music out of the orchestra's history: Kindler's transcription of a Toccata long said to be by Frescobaldi but now known to have been composed by one of Kindler's cello colleagues, Gasper Cassado. Regardless of its provenance, it is a handsome work whose pseudobaroquery would not fool anyone. It made an impressive opening, played with resounding resonance from the large orchestra for which Kindler cast it.

Next came music by one of the founding spirits of the orchestra, Mary Howe, who was a distingquished composer as well as an indefatigable supporter of Kindler and the infant NSO. Her "Stars" is a brief, beautifully worked tone poem filled with impressionist lights and shadows that deserves to be heard more often.

Walter Piston's music often appeared on National Symphony programs, frequently very soon after being written. In 1944 Kindler gave the world premiere of Piston's Second Symphony, with which Rostropovich concluded the first half of the opening concert. Today the music sounds a touch Ives-ish, a bit ragtime-jazzy, and in the eloquence of the slow movement with its glorious long line for the strings, genuinely noble.The later Piston symphonies are finer works, but this has a kind of raw, Americana sound that is a fitting reminder of the times out of which it was born. The playing was appropriate to the changing moods.

Finally there was the Shostakovich, with which Rostropovich garnered some of the orchestra's most overpowering ovations on its July trip to South America. Last night he and the orchesta recreated all of the beauty and the excitement that brought him a half-hour triumph in Buenos Aires. It was a thundering close to the fine opening concert.