On the top of every music enthusiast's weekend agenda should be this Saturday night's Back Society Orchestra Concert. In this, the third of their five seasonal concerts, the group will tackle three infrequently heard compositions of three infrequently heard compositions of three of the most popular composers in music history: Brahms's "La Scala di Seta" and Beethoven's Piano Concerto 7/8 2. Featured soloist will be pianist Richard Kogan who will also perform Beethoven's stormy "appasionata" sonata at the pre-concert recital beginning 7:45.

THURSDAY

Organ Recital by James Johnson music director of the First Church in Cambridge. Busch-Reisinger Museum, 12:15.

FRIDAY

Tamara Mitchel, soprano, Keith Cheng, piano, and Stephen Lichten, clarinet, perform songs of Shubert, Spohr, Brahms, and Strauss. Kirkland JCR, 8:30.

Kuumba Singers perform under auspices of the Harvard-Radcliffe Afro-American Cultural Center. Memorial Church, 8:00.

George Loring, piano, plays Schumann "Papillons" and Brahms F minor piano sonata. Dunster Library, 5:30.

Sonatas and variations for cello and piano performed by Robert Osman, cello, and Carl Kaufman, piano. Eliot Library, 7:30.

SATURDAY

Bach Society Orchestra performs Brahms Serenade, Rossini Overture, and Beethoven Piano Concerto 7/8 2. Neal Stulbert, conductor, Richard Kogan, piano soloist. Pre-Concert recital: Beethoven piano sonata in f minor, the "Appasionata" performed by Kogan at 7:45. Sanders Theater, 8:30.

John Eisenhart, french horn, and Hsueh-Yung Shen, piano, perform music of Mozart, Kreisler, and Debussy. Holmes Hall, 7:30.

SUNDAY

Sheila Rheinhold, violvin, and Max Sung, -iano, perform music of Mozart, Kreisler, and Debussy. Holmes Hall, 7:30.

Cecylia Arzewski, violin, and Eva Hoffman, piano, together play works by Bach, Beethoven, Prokofieff, and W ieniawski. Currier Senior Common Room, 3:00.

Paino trio music of Schubert performed by Irene Bertozzi, violin, Robert Osman, cello, and Carl Kaufman, piano. Adams Lower Common Room, 4:00.