American-born pianist Stephen Bishop-Kovacevich's manner of playing resembles that of a prize-winning gymnast: muscular, with great flexibility. In his recital yesterday afternoon at the Masur Auditorium of NIH, this power and agility were tested in late-period works by Beethoven and Schubert.

While all of the pieces bridged the gap between Classical and Romantic modes of expression, the temperaments exact different demands from the interpreter. Beethoven's Six Bagatelles, Op. 126, is almost epistolary in nature; concise, hectoring, droll and a bit crude, it strikes with the force of a locker-room pep talk with none of the expletives deleted. Rumbling ostinatos clash with abrupt lyrical interludes, which in turn yield to surprise, Haydnesque pauses. Bishop easily wound his way through these intricacies, attentive to the gradations in dynamics.

For Beethoven's Sonata in A Major, Op. 101, he melded a carefully drawn meditative tone with explosive chords, so that the dream-like passages never lulled the audience into complacency. His treatment of the final movement dissected the artful canon, so that all the inner voicings could be clearly heard. The only distraction--and it occurred in both the Beethoven pieces--was his nervous tapping of his heels in anticipation of movement to the pedals.

Schubert's Sonata in B Flat Major, his last work in this genre, contained little of the Beethoven brashness. The melodic ideas spin out endlessly, and repetitive trills in the left hand punctuate thematic shifts. Bishop had no trouble following Schubert's design; at one point he raised his left hand in a poetic, swirling fashion, as if to draw the last ounce of emotion from the piano. He almost succeeded. Fortunately, he saved some for a well-deserved encore of a Mozart minuet.