Pianists tend to approach their mighty instrument in one of two ways. Either they view it as a sleeping genie ready to leap to their service or they see in it a giant waiting to be overcome. Definitely a member of the latter category, pianist Jacquelyn Helin attacked the Bo sendorfer at the Corcoran last night with muscular fury, sometimes emerging victorious and sometimes not.

Helin laid out an impressive plan of battle by choosing three demanding works -- Copland's Sonata of 1941, Beethoven's A-Flat Major Sonata, Op. 110, and Schumann's "Carnaval." To the Copland she brought a bright, hard-edged tone appropriate for the sinewy style that characterizes much of the piece. However, she failed to let down her guard enough to allow the music's lyrical moments to surface or, in the final movement, its spaciousness.

Despite evidence of thoughtful preparation and careful deployment of forces in both the Beethoven and the Schumann, the results proved disappointing. Though Helin's tone was big, it was never rich or warm. Too often technical rather than musical concerns seemed to dominate the pianist's thinking. Surprising little slips -- a rhythm not quite clear, a bass note missed -- cropped up, belying Helin's command over her instrument. Yet one suspects that such difficulties are more mental than actual. By shifting her focus to expressive goals, Helin might come to a more congenial relationship with the piano and realize a more satisfying performance.