"I view this change as a natural evolution in the career of an orchestra conductor," he added. "The goals which I set when I began my tenure here will have been accomplished. In my opinion, the NSO now ranks amongst the world's great orchestras‹a point of immense pride for me and all the members of the orchestra."

Earlier this year, Slatkin, 60, left the BBC Symphony after a four-year term as chief conductor. He was the music director of the St. Louis Symphony from 1979 through 1996, and remains conductor laureate of the SLSO.

During his tenure at the NSO, Slatkin has championed American music, commissioning 64 new works from American composers, and had led tours of Europe, Asia, and the United States. Among his five Grammy Awards is the 1996 prize for Best Classical Recording, won for his first recording with the NSO. He is also the founder of the National Conducting Institute, held annually at the Kennedy Center, the NSO's home.

"Leonard has done a remarkable job of building the quality and standing of the National Symphony Orchestra.," said NSO chairman Ann Jordan in a statement. "He has given NSO audiences hundreds of thrilling nights in our concert hall."

The NSO board is in the process of forming a search committee to seek Slatkin's replacement.