MUSIC

Leonard Slatkin, whose contract as music director and conductor of the St. Louis Symphony Orchestra was scheduled to end in 1991, will stay with the symphony for an additional two years through the 1992-93 season, it was announced Thursday. Slatkin, born and reared in Los Angeles, became assistant conductor of the symphony in 1968 and assumed his current post in 1979. Slatkin and the St. Louis Symphony have signed exclusive, five-year, multi-disc recording contracts with BMG Classics, the international recording company that includes RCA Victor Red Seal. The contracts call for more than 30 recordings.