Last night's Library of Congress program added another Belgian revelation to the many arising from the Belgium Today celebrations currently all about town. Pianist Peter Orth and violinist Rafael Druian presented with infectious enthusiasm a throughly engaging sonata written in 1925 by the virtually unknown Belgian composer, Albert Huybrechts.

To say that the sonata combined with harmonic language of Debussy with the rhythmic vigor of Stravinsky is merely a means of pinpointing its material. The actual work represented a fresh and individual combination of the vocabulary of Huybrechts' time. Confident in tone, and freely flowing, the sonata would make a highly pleasing addition to the chamber repertoire. One suspects that Huybrechts might have become better known had he not died at the age of 39 in 1938. This particular sonata won the Elizabeth Sprague Coolidge Prize in 1926.

Opening with Mozart's last violin-piano sonata and closing with Brahms' first sonata for that combination, Druian and Orth were superbly matched. Druian's depth and Orth's intensity blended, each influencing the other, to produce playing of the highest quality. The older Druian is a familiar figure in the concert world, and Orth will undoubtedly become so in time. The winner of last year's special Naumberg Piano Competition, he is an extraordinary pianist and fine musician. Both he and Druian exhibited that rare capacity to find in the limitations imposed by the composer complete freedom of expression.