Nashville will host the National Folk Festival, billed as the country's longest-running traditional arts event, for three years beginning in 2011, organizers announced today.   The festival will bring at least six stages of continuous music, a dance pavilion, crafts, regional food, storytelling and folklife demonstrations to downtown Nashville for a three-day event that's expected to draw 80,000 people in its first year. Exact dates and locations haven't been decided. "It will be an event that includes the very finest traditional artists from across the nation, and at the same time, includes the best of Nashville and the best of Tennessee," said Julia Olin, executive director of the National Council for the Traditional Arts, which puts on the festival. Nashville beat out 40 cities to host the event, which travels around the country in three-year blocks. It's currently in Butte, Mont. The festival, which began in 1934, will celebrate its 75th occurrence in Nashville. It was last here in 1959. In some cities it has visited, among them Richmond, Va. and Dayton, Ohio, the festival has left behind a locally produced event that carries on the tradition of celebrating folk culture. Organizers hope the same happens here. "You can never have too much free music and live music in Music City," said Mayor Karl Dean, "and this event in particular will draw people of all ages and backgrounds."