In his concert at the Terrace Theater last night pianist Emanuel Ax conducted a sustained exploration of the mystery of communication through sound. His interpretations of Beethoven's Sonatas No. 15, 17, 22 and 23 unfolded like a meditation on the power of music. And no listener seemed more struck by the wonder of this language than Ax himself.

Beethoven, who produced possibly the most intense writing of any composer in Western culture, proved ideal material for Ax. Treating each of the sonatas like a single, vast exposition, Ax delved for their connecting threads even as he pursued their emotional extremes. With brilliant insight he revealed the underlying continuity of Beethoven's concepts, repeatedly showing that pauses and formal divisions existed only on paper and not in the composer's mind.

For the opening D-Major Sonata, Op. 28 ("Pastoral") Ax found a veiled tone quality, especially in the first movement, that served as an ideal evocation of the work's inner poetry. The following D-Minor Sonata, Op. 31, No. 2 ("Tempest") further demonstrated his virtuosic control of touch and tone and the sure esthetic purpose with which that command is used. The special clarity of Ax's playing stems from his fine sense of just which motif, harmony or line to stress in order to underline its direction at any given moment. The precise manner in which he conveyed the obsessive quality of this sonata's monothematic final movement proved one of the evening's high points.

He rejoiced in the articulate and rather extroverted style of the F-Major Sonata, Op. 54, and then plunged into the F-Minor Sonata, Op. 57 ("Appassionata"), with his awesome resources into a climatic close for the evening.