The Kennedy Center's summer Festival of Festivals is proceeding apace. Last night brought the opening of the Aspen Music Festival's series to the Concert Hall, six evenings of music for chamber ensembles of various sizes, played by the college-age participants in Aspen's marvelous summer program.

For this concert, Jorge Mester led the Aspen Chamber Orchestra in the original version of Copeland's "Appalachian Spring," Mozart's G Major Piano Concerto, K. 453, and the Symphony in C Major by Berwald.

This may be a small orchestra, and a young one, but it has a big sound and the musicians play with understanding and imagination. The Copland, for just 13 players, was distinguished by a compelling combination of intense concentration and graceful agility.

The Mozart, with Misha Dichter as soloist, was more matter-of-fact. Dicter was playing a brittle-sounding instrument that conveyed more in the way of nimbleness than warmth, but, nevertheless, he managed some lovely duets with the winds in the slow movement. Mester, a master of eloquent baton technique, drew nice ideas from the inner voices.

Almost as a reward for its earlier restraint, the orchestra lavished all its romantic inclinations on the lush sonorities and broad expanses of the concluding Berwald, a generously orchestrated piece flavored with Scandinavian spaciousness.