Last night's audience at the Library of Congress was invited to stretch its minds and ears with an intriguing program of music for pianos and percussion. Conducting this exploration of new sound were four able guides: duo pianists James Freeman and Gilbert Kalish and percussionists Raymond DesRoches and Richard Fitz, for whom the music was originally written.

Of the three works performed the most interesting by a large measure was Ken Hosley's Musings on E for two pianos and percussion, which received its premiere last night. Born in 1949, Hosley is a former student of percussionist DesRoches. On first hearing Musings came across as a fascinatingly elusive work, full of rhymthmic subtleties and shifting colors. The music flowed in a continual state of becoming, avoiding movement toward any fixed point. Though serially derived the results were poetic and moving. The intricacies of the work seemed to have been well handled, although the pianos were often overshadowed by the percussion sounds.

Also receiving its premiere last night was Roger Reynolds' Less Than Two for two pianos, percussion and tape. Born in 1934, Reynolds has written many works involving electronic sounds and is currently based in California. Less Than Two was like a kaleidoscope of fragile sounds continually forming into a pattern and then breaking up into new arrangements, echoing yet not repeating what had gone before. The tape sounds were cleverly used as a kind of drone moving in and out of focus as the music developed.

The concluding work, George Crumb's Crumb's Makrokosmos III, which was premiered by these players in 1974, seemed almost tame, its structure readily accessible.