There were special glories in last night's Kennedy Center concert by the National Symphony Orchestra. Mstislav Rostropovich was back to conduct the world premiere of the Ninth Symphony by Peter Mennin, and Maurizio Pollini was the soloist in a performance of the Fourth Piano Concerto of Beethoven that held much unusual beauty.

The new Mennin symphony was commissioned by the National Symphony in observance of its 50th anniversary. It is a stunning achievement and one likely to quickly win a place among the most admired symphonies of our time. It is cast in three relatively brief movements, the first two of which are slow: a leno non troppo followed by an adagio arioso.

From the first notes of the brooding opening it is clear that Mennin wrote in a mood of expansive lyricism. That lyricism alternates, as the first movement develops, between clustered chords from the winds and some immense agitation in the strings, in writing of the utmost virtuosity.

Following an enormous eruption at the peak of the movement, there is a luminous passage of exquisite radiance from the massed strings. The slow movement is, as its marking suggests, openly songful, a poignantly expressive sustained passage in which the plangent oboe has a lovely solo.

The finale is a turbulent outburst, taken at a furious pace, with the entire orchestra in dazzling episodes reminiscent of the explosive power of "Sacre de Printgemps." It is a triumphant close to an intensely personal score. Rostropovich conducted the symphony with ardor and was rewarded with some superb playing. The repetitions this week should add to the excitement that increases as the work progresses.

With the orchestra appropriately reduced for the Beethoven Concerto, Pollini played with soverign perceptions, matching his deeply poetic touch and sensitivity to technical brillance that made the grand movements memorable. aThe cadenza to the first movement was of particular impact, while the slow movement was, from both orchestra and piano, an ideal dream.

The evening opened with the orchestra's first performance of Rimsky-Korsakov's early symphonic suite, "Antar." If the music paled in the light of what soon followed, there were frequent opportunities for beautiful solo playing from harpist Dotian Carter, flutist Toshiko Kohno, and Loren Kitt's clarinet. Each took full advantage of the openings. If the second movement were dropped, the suite could be a welcome substitute for "Scheherazade."