A full-size, all-volunteer orchestra is becoming a rarity. Out of the six in Northern Virginia, only the McLean Symphony, under music director Dingwall Fleary, has maintained that status.

That group performs some important roles in the community by providing a stage for amateur, part-time or young musicians and also by playing a more diverse repertoire than can symphonies who have to pay greater attention to the bottom line.

In addition to a regular subscription series, the group also gives periodic chamber music concerts in an informal setting featuring the players in the orchestra. One announced purpose is to acquaint people unfamiliar with classical music to the art form, but in a friendly environment.

This is a noble goal. But there were some serious problems with the execution as evidenced by the chamber concert Sunday night at St. Luke's Catholic Church.

First, a musical performance to a paying public (and the tickets cost a rather hefty $12 a person) should meet certain minimal standards. Unfortunately, the performance of Mozart's Piano Quintet with Woodwinds, which opened the program, did not do even that. The piano part was played with a disregard for even the basics of phrasing and tone; the horn was too loud, and the bassoon too weak. There was some good work by clarinetist David Hughes, but it was not enough to turn the tide.

Schumann's Piano Quintet, Op. 44, was a bit better, but far from adequate. Violist Jeanne Rosenthal was a pleasure to hear (fortunately Schumann gave her plenty of good lines), but the cello sounded insecure and thin and provided absolutely no support. The violins were of average quality and, for the most part, on pitch.

Fleary played the dominant piano part with good instincts but with little apparent direction and far too many missed notes. He has enough technique and musicianship to do much better. In some places the rhythmic patterns were way off: long sections of crisp dotted rhythms (say to yourself, fast: DUM-um-um-Dum-DUM-um-um) were erroneously played in perfect triple rhythm (DUM-um-Dum-DUM-um).

The final work was Suite for Flute and Jazz Piano, a crossover jazz-classic work by Claude Bolling. Guest artists Jeff Cummins on piano, Chris Enghauser on bass and Marshall Maley on drums joined principal flutist Sharyn Byer in a sparkling and well-wrought performance -- the only one of the evening. It is ironic that a sensitive but naive listener would have walked out thinking that classical music is dull and sloppy but jazz has lots of pizazz.

Other problems: The piano was embarrassingly out of tune. Fleary's commentary between numbers was long and (no doubt unintentionally) patronizing, condescending and, in the case of an endless discussion of clearing wind instruments of condensation (so-called "spit valves"), silly. His historical information on the compositions, however, was interesting. There was a lot of talk about why audiences are discouraged from applauding between movements of a single work, and that we should feel free to applaud when we wanted to. So people tended to give desultory applause that came neither from the heart nor from knowledge that the piece was over.