The Camerata Bariloche of Argentina is a chamber orchestra of 16 strings, which, from time to time, calls on solo oboe, horn and harpsichord. Last night they placed in the Kennedy Center's Terrace Theater in a program that ended in a triumphant account of the Tchaikovsky Serenade for Strings.

In this familiar music the massed sound of the string ensemble took on an appropriate refulgence and spirit. It was a pleasure to hear the elegance and clarity of Tchaikovsky's writing in the lighter sound afforded by the chamber group.

The concert opened with a Vivaldi concerto for solo violins and continued with Bach's concerto for oboe and violin. Without a conductor, the phrasing was at times a bit on the square side, tending to lack differentiation from one composer to the next.

Mozart appeared twice on the program: once in a charming rondo for horn and strings, with Guelfo Nallil doing virftuoso service on the horn; the second time unexpectedly, because the music of three Argentine minuets by Alcorta, Esnaola and Alberdi, was somehow lost. In its place harpsichordist Monica Cosachov stepped in with a brief Mozart concerto movement heard to advantage over a quartet of strings.