On Oct. 17, jazz legend Ella Fitzgerald is featured in the first of a free series of rarely seen jazz films and videos that will be shown through Dec. 19 in the Mary Pickford Theater. The series will showcase all styles of jazz, from Louis Armstrong and Bix Beiderbecke to John Coltrane and Don Cherry, and the individual programs will be hosted by some of the nation's top musicians, scholars and critics. The 7 p.m. event will be introduced by Rep. John Conyers of Michigan and Keter Betts, who was Ella Fitzgerald's bassist for more than 20 years. Admission to the films in the Pickford Theater, third floor of the Madison Building, is free, but telephone reservations are required. Call (202) 707- 5677 during business hours (Monday-Friday, 9 a.m. to 4:30 p.m.).