The trombone is not the most elegant of instruments. Of unwieldy shape and size, and requiring cumbersome paraphernalia to increase its limited tonal possibilities, it is normally relegated to the back row of the orchestra.

So it was not surprising that there were a few giggles when principal trombonist Milton Stevens strode center stage at the Kennedy Center Concert Hall last night and stood between two music stands laden with mutes, ready to perform with the National Symphony in a concert featuring its own orchestra members as soloists.

But Robert Parris' Concerto for Trombone, Wind Quartet, Piano, Percussion and Strings quickly set an ominous mood. Ethereal high string sounds punctuated with violent thuds from the bass drum created a background for speechlike trombone dialogues with the other instruments. Stevens played brilliantly, displaying mastery of the instrument in the complex, fast-paced finale.

Sweet-toned clarinetist Loren Kitt deftly negotiated the twists and turns of Weber's Concertino in E-flat, and harpist Dotian Carter brought tonal variety to Debussy's "Danses sacre'e et profane." John Martin's light and flexible cello was perfect for Boccherini's Concerto in B-flat, performed from the romanticized but effective Gru tzmacher rewrite.

Mstislav Rostropovich opened the program with a rousing "Concert-Polka" by Lumbye (a contemporary of Johann Strauss), featuring skilled violinists Hyun-Woo Kim and Dennis Piwowarski, and closed with a wonderfully controlled, clear and thus unusually exciting interpretation of Ravel's "Bolero."