The 40th anniversary season of free concerts at the Phillips Collection opened yesterday afternoon with a winning example of the kind of programs that have long marked the Phillips as one of the country's top concert halls.

Violinist Jody Gatwood played a solid, conservative list that began with the unaccompanied Bach sonata in A Minor, proceeded to the E Flat Sonata of Beethoven, and the D Major Sonata by Prokofiev, before closing with the Ravel Tzigane.

Ruth Balis was Gatwood's admirable pianist. She offered playing that matched the violinist's in style and musicianship, although there were times when she was a bit more subdued than best suited the music, as for example in the Beethoven, which is marked "for piano, WITH violin." And again in the Prokofiev, the basic harmonic foundation was sometimes unclear because of a lack of weight in the piano.

To say that Gatwood's playing was all that his demanding program required is saying a lot about this distinctive musician, but it is true. He is unfailingly musical in every impulse. That is as apparent in his building of Bach's architecture as in the imitative manner of Ravel's gypsy piece. He presented the early Beethoven sonata with a restrained approach that was ideal, but opened up in broadly spacious style in the largest pages of the Prokofiev. His tone is constantly a thing of beauty, taking on particular radiance in such moments as the opening of the Prokofiev. He fills phrases with nuances while always being sure to make music in everything he touches. These are unusual gifts.