Tonight at 7:30 at Severance Hall, pianist Mitsuko Uchida sits in with the Cleveland Orchestra to play Piano Concerto No. 3, the most popular of Bartok's three piano concertos. The concert will also include Schubert's Mass in E-flat Major. Guest speaker Cicilia Yudha, associate music prof at Youngstown State University, will give the free pre-concert talk at 7. Performances take place at 8 p.m. tomorrow and Saturday. Consult the orchestra's website for more info. (Niesel)