Pianists, some say, may be divided into those who pound on the keyboard and those who do not. In her concert at the Phillips Collection yesterday, Nelita True was a true pounder.

Her undeniable strength was obvious from the first of two Scarlatti sonatas with which she opened the program. Yet, messy trills and spotty phrasing marred the F Minor, K. 481, while rhythmic control and sheer insistence made the F Major, K. 482, quite a lot of fun.

True's musicl diction often created a meaning of its own which was not always the composer's. This became more objectionable as she approached Beethoven's music. The Sonata in G Major, Opus 31 No. 1, caught Beethoven in a rare mood of shallow glee, which is not to say that it is easy to play. On the contrary, the score calls for both humor and dainty precision, lest the sonata fall into self-parody or low-grade Rossini. True took the opening of the first movement at a rushed, loud gallop that augured well for the rest, but the promise remained unfulfilled.

The second movement, curiously called "Allegro grazioso," contains more trills than are usually encountered in a bel canto mad scene, and most of these were approached with little elegance or virtuosity by the pianist. Only the end of the final rondo caught the mood of the score, phrasing the close with a musical wink.

Debussy's "L'Isle Joyeuse" suffered the most from the pounding style. All the notes seemed to be there, but few phrases were to be heard in this performance, which laced the passionate tonal sweep that is the heart of this music. The program also included works by Brahms and Chopin.