When the Juilliard Quartet performs, one gets the feeling of being taken through a number of very physical and somewhat neurotic experiences, while the Concord String Quartet, as heard Friday night at the Library of Congress, exists on total cooperation among its members with gestures much more relaxed and natural, as the music is literally wafted from one player to the next.

George Rochberg's Cello Quintet (1981) compulsively concerns itself with a certain kind of accessibility in the same vein as his "Confidence Man" opera, which premiered in Santa Fe last summer. The result annoyingly brings up the fact that modern music refuses to be easy-listening music, and an attempt at such a mixture always succeeds in inducing to slumber lovers of any and all kinds of music. Some may have mistaken the piece for an anxiety-ridden musical melodrama with a solo part for lamenting gypsy violinist. Helping to salvage some special moments from this composition was guest cellist Sharon Robinson, who proved herself to be expressively and technically on a mutual plane with the expertise of the Concord.

The quartet was allowed to show its true colors in a performance of Haydn's Quartet in F minor, Op. 20, No. 5. This piece, which contains an unusual amount of polyphony for such a composer, was translated as a virtual conversation of delicacy and grace. First violinist Mark Sokol was masterful at blending his predominance of solo melodies with the rest of the ensemble.

The entertainment was completed with a very curious work by Dvorak: "The American" quartet, which allegedly was written in 16 days during a vacation in Iowa. A new environment for this Czech composer spurned the vast sound in this piece, probably reminiscent of the open spaces of the Midwest in 1893. Appropriately, the work was strongly performed, as cellist Norman Fischer's rag mop hair and violist John Kochanowsky's wiry form were set into motion.