The subject of "replacement" players has been making headlines lately in the sports world. Wednesday night it proved newsworthy in an arena as unlikely as the Terrace Theater, where the Guarneri String Quartet had suddenly become a piano quartet. Pianist Steven De Groote filled in for first violinist Arnold Steinhardt, sidelined after elbow surgery, and an all-Beethoven program was scrubbed in favor of piano quartets by Mozart and Schumann.

De Groote and the Guarneri players established a favorable rapport, but not without some initial friction. The pianist's domineering bright tone in the opening movement of Mozart's G Minor quartet contradicted the philosophy of separate but equal voices followed elsewhere in this piece and in the lovely Schumann E-Flat quartet. The group wrung every last note of lyricism from Schumann's score, and the bold, warmly reassuring viola and cello parts received careful attention from Michael Tree and David Soyer.

The three Guarneri strings greeted Beethoven fanciers with the Serenade in D, Op. 8, entertaining music filled with grace and wit in the manner of Mozart and Haydn. Their splendid performance was rendered poker-faced, which merely added to the comic intensity of the bumptious march and scherzo movements.