There is a great deal of fine music-making going on in this year's Summer Chamber Festival at the Library of Congress, both in the spontaneity of the ensembles and in marvelous attention to detail by individual artists. Both of these came together last night in the performance of the Mozart G Minor Piano Quartet, in which pianist Barbara Weintraub found an astonishing variety of attacks and ways to weight her lines while the strings moved through the music with decisive individuality. It took a couple of measures for the rhythmic shape of the second movement to come into focus, but the rest was quite lovely.

The opening "Ma Me`re l'Oye" by Ravel, played by Weintraub and Edmund Battersby in its original form as a duet for piano four hands, set the stage, in its colorful palette, for both Benjamin Lees' Sonata No. 2 for violin and piano, and the Mendelssohn B-flat Major String Quintet.

The sonata is an intense work that maintains, within its three contrasting movements, remarkable unity of idiom. Violinist Junko Ohtsu, who has an outstanding bow arm, needed all its power and fluidity to navigate the music's rocky terrain. Lees was in the audience to acknowledge the audience's delight in both the music and the performance.

The concert ended with an exuberant performance of the Mendelssohn, led by cellist Peter Wiley's irresistible propulsion. Wiley will be replacing the retiring Bernard Greenhouse in the Beaux Arts Trio next season, which promises to be an ideal matching of temperament and musicianship.