A new member of the Wolf Trap family was introduced to a good-sized audience yesterday afternoon when the Concert Soloists of Wolf Trap played their first concert. It was an auspicious opening to a new venture.

Gary Schocker gave a first-class curtain-raiser to the program in the A Minor Partita for solo flute by Bach. The young man plays with real style, a big tone, easy technique, and a kind of exuberance that suited the music. Here and there a note flew off into the friendly woods, but in view of the humidity that hung around all afternoon, that was hardly surprising. Rampal himself had similar problems last year.

Claude Debussy, who in his critical writings was continually calling for more music out-of-doors - "from the trees," he insisted - would surely have been pleased with the mockingbird who turned his trio-sonata for flute, harp and viola into a quartet. For it, Schocker was joined by harpist Gloria Agostini, and Oscar Shumsky, who, forsaking his usual violin, took up the viola which he plays quite as compellingly. Though the music was at times a bit diffused in the open air, Debussy's richly introspective vein was poetically explored.

Shumsky returned with pianist Earl Wild, the music director of the Soloists, to play the Kreutzer Sonata by Beethoven. After some years of not hearing Shumsky's manner and tone, it was a distinct pleasure to enjoy again his complete command.

Nowhere was his authority more touching than in the opening of the variations. In his big playing, Wild offered his listeners a reminder that Beethoven marked these sonatas "for piano with violin," but he was always in fine balance.

The concert closed with the neglected trio of Tchaikovsky, a work of benevolent length, some undue repetition, but great melodic and concerted beauty. The work brought out another of the ensemble's excellent younger players, cellist Charles Curtis, who made the frequent dialogues with Schumsky moments of unusual beauty.