A Washington-based group, Le Quatre Percussion Quartet, played a notably unconventional concert at the Kennedy Center's Terrace Theater yesterday afternoon.

As its title suggests, there were four players. The group was led by Alfonso M. Pollard. But after the question of numbers, any analogy, to, say, a string quartet, breaks down. There were not just four instruments. This observer counted 37, and since anything from a loose tooth to the ring on your finger can classify as percussion, that estimate may be way off.

This performance by Le Quatre has two purposes. One is, in Pollard's words, "to increase acceptance of contemporary percussion music as a serious art form by highlighting the ensemble's vast musical and technical diversity, thus ensuring high public visibility, impact and support." This statement came in the program book of the Kennedy Center, which sponsored the concert.

The other purpose is, quite simply, to give a prominent public forum to aspiring percussion players, of whom there are today far more than the symphony orchestras of the country can employ.

Yesterday's concert reached its high points with some Scott Joplin and something quite different.

The Joplin was an arrangement for xylophones of four rags. There wasn't the addictive gusto of Joplin's irresistible originals as written for piano. But these versions did have a curiously trance-like euphony; one wonders what Joplin would have thought.

The quartet also played a large-scale nonet for percussion and brass by William Kraft. It sounded a bit like Hindemith--hardly an unfriendly observation in music written for brass. There was Hindemith's frequent habit of scoring brass instruments in unison and also his delight in playing two instruments against each other in fugato style.

For all this pleasure, though, the fact remains that however virtuosic the player in such a percussion ensemble, the classical literature for this combination of instruments is slender, which the rest of the music on the program demonstrated. Maybe this is inevitable, given the central role of the percussion battery to provide rhythms and sonorities in the symphony orchestra, with a neglect for whatever capacity they may have for harmony and counterpoint.