* The Claremont Quartet plays tonight Beethoven's Quartet in A major, Opus 18, no. 5; Quartet in E flat major, Opus 74; Quartet in F minor, Opus 95; and Quartet in F major, Opus 135. (Sanders Theatre, 8:30 p.m.)

* Opening in Lamont Library today is an exhibit of the theatre in Brazil, arranged by Emilio Fontana of the International Seminar.

* The bus for the Summer School's Tanglewood Tour leaves Thayer Gate at 1 p.m. tomorrow.

* A square dance will be held Tuesday in the union, 8:30 p.m. (Admission free.)

* Busch-Reisinger Museum presents in its garden daily recorded music concerts, 1-2 p.m. Next week: Gluck's Orfeo, Milhaud's Sketches for Woodwinds (after Wateau), Duke's Surrealist Suite, MacDowell's Woodland Sketches (the last three works are related to art), Mozart's piano Concertos no. 21 and 27, and Rameau's Les indes galantes.

* Christ Church in Boston continues its garden concerts and recitals with organ music by John Fesperman, next Wednesday at 8 p.m. (Five passacaglias by Frescobaldi, Muffat, Buxtehude, Cabinilles, and Bach.)

* The First Church of Christ, Scientist, in Cambridge, announces a lecture tonight on Christian Science by Gertrude E. Velguth of flint, Mich. (8 p.m.)

* The recorded music session from 3-5 p.m. in Matthews Hall Saturday will present Brahms' Academic Festival Overture, Opus 80; Schubert's Quintet in C minor, Opus 163; and Mendelssohn's Symphony in no. 4, Opus 90 (Italian) and Symphony no. 5 in D minor, Opus 107 (Reformation). Ba Thwin, a Burmese visitor, will play recorded music from Burma Sunday at 3 p.m.