The Concert Soloists of Wolf Trap are an interestingly assorted quartet: flute, cello, harp, and piano. They were brought together last year as a resident chamber group of Wolf Trap's summer season by pianist Earl Wild. Joined by violist Aaron Rosand and pianist David Korevaar at the Library of Congress last night, they presented what is to be hoped was not a preview of their summer activities.

It was a concert that, on the whole, sounded poorly rehearsed and slipshod. Only the concluding Barber Cello Sonata, played with intensity and conviction by Wild and cellist Charles Curtis, had real musical interest.

Curtis has a big, rich sound that he laces with a rather wide vibrato, but he moves it with accuracy and sensitivity.

In its first performace, "Concerto for Three Instruments (Of Time)" by David Kosis for flute, cello and harp, proved to be frisky and pleasant 20 minutes of not very memorable contrapuntal textures, in which the harp had a tough time competing with the rest of the group.

The concert opened with a dreadfully uncoordinated performance of a Mozart sonata for four hands, and the Brahms that followed was sleeker but not much more satisfying. It was the D Minor Violin Sonata, played by Rosand and Wild with the kind of remoteness that one might expect from the collaboration of two strangers. It was an odd experience.