With the confidence born of strength, pianist Boris Bloch set for himself challenges of subtletyu rather than virtuosity in a recital at the Terrace Theater Saturday afternoon.Tall, with large hands, Bloch looked almost too large for his instrument, as he scrunched down over the keyboard for the oepning Haydn and early Beethoven sonatas. With Stravinsky's "Serenade en La" he unfolded halfway, finally revealing his full measure -- both musically and physically -- in the closing group of Chopin selections.

Another in the cluster of Russian pianists who have emigrated to this country within the last few years, Bloch was born in Odessa in 1951 and made his New York debut in 1976. It is a tribute to his seriousness as an artist that (if Saturday's program was typical) he has chosen to avoid the easy route which his technical facility offers, bypassing flashy displays to confront deeper interpretive problems. His playing is distinguished by a constant striving for control and meticulous attention to expressive detail. There is virtuosity, but it is securely tied to musical ends.

Though his approach to the classical period has not yet fully matured, Bloch brought a probing, refined sense of anticulation and touch to the Haydn and Beethoven works. A sharply honed concept and strong finger work made Stravinsky's "Serenade" sparkle. And Chopin's ideas glowed as Bloch with sure insight applied his fluid technique to the flowing phrases.