The paucity of compositions for violin and viola is not difficult to explain. The timbres of the two instruments make perfect blending almost impossible, unless the violin is stripped of its brilliance, or the viola is forced to produce sounds not indigenous to it. Many concert artists are unwilling to make the necessary compromises, and most composers, fearing neglect, channel their talents elsewhere. But yesterday's recital by Joseph and Lillian Fuchs demonstrated that music in this medium does deserve a place in the concert hall, and does respond to sensitive, balanced performances.

Mozart's Due in B-flat is numbered 424 in the Kocchel catalog, but it sounds much carlier. Mozartean good spirits are here in abundance, but the work lacks a melodic and rhythmic inventiveness. Mr. Fuchs and his less famous but thoroughly accomplished sister reached the heart of the music from the very start. They played with precision, but not of the machine-gun variety. Every phrase received individual treatment, according to what preceded and proceeded it, as well as to its own unique factors. In addition to being consistent with the music, the two interpretations were consistent with each other: a situation that prevails only in the finest of ensembles.

Even in this comparatively minor work, Mozart exhibits his uncanny scoring ability. The instrumentation is perfectly suited to the music, and no other combination seems possible. Such is not the case with the other duo work on the program, Martinu's Three Madrigals. This is good, strong stuff, but has little instrumental logic. Of course, not all local color is eliminated, and there are several very impressive effects: the viola is often used as a percussive instrument, and the skilful utilization of mutes gives an eerie flavor to the second madrigal. But nearly always, another instrument would have been equally effective. It seems to me that a piano could have been used to great advantage in many places. And a slithering melody in the third madrigal might have been overpowering on a clarinet or saxophone.

The music itself has a tremendous amount of motion and harmonic variety. It sounds almost atonal at times, but I suspect this is due largely to the sudden, rapid shifts in tonality. Textural variety is achieved by frequent solo passages in which one of the instruments takes a long, vocal line with semi-estinato accompaniment. Taken as a whole, the Three Madrigals may very likely become a permanent part of the violin-viola repertory.

Any performance of the Chaconne from Bach's D minor Partita is bound to fall short. The notorious difficulty of the piece makes it virtually unplayable, and any evaluation must be based on a comparison with some mythical perfect performance. Criticism thus becomes even more subjective than usual. Mr. Fuchs' idea of the music as a gradual build-up in tension followed by a gradual release, with regularly-spaced interludes of quasicommentary, is extremely provocative. His failure to sustain and integrate this conception was caused primarily by the physical demands of multiple-stops and prodigious leaps that frequently leave interpretation behind.

Miss Fuchs fared somewhat better in her selections from Bach's suite in E-flat. Originally written for cello, many of the difficulties are minimized by using the smaller instrument. I disliked her phrasing in the Prelude, but in matters of tone and technique, she was almost as good as the music she played.