The Key will follow its engagement of "The Battle of Chile" with a series of Cuban films. Eight features, including "The Last Supper" - a new film by Tomas Gutierrez Alea, the director of "Memories of Underdevelopment" - and "Cantata de Chile" - a new film by Humberto Solas, the director of "Lucia" - will rotate in repertory for a week beginning Wednesday, May 3. On May 10 "The Last Supper" will begin an exclusive, open-ended engagement on its own.

A delegation representing the Cuban Film Institute is scheduled to arrive in Washington on the opening day of the series. This party will consist of Santiago Alvarez, vice president of the institute; Mayra Vilasis Rodon, a film critic and writer; and Alina Sanchez Rodriguez, an actress. They also are accompanying the series to Los Angeles, San Francisco and New York.

Moonforce Media, a local feminist group organized to produce and distribute nontheatrical films by and about women, has packaged two new programs for the National Women's Film Circuit that will be launched with public showings at the Ontario. Starting times are 7 and 9:30 p.m. on Thursday, May 4, and Saturday, May 6. According to the sponsors, "Everyone is welcome to attend Thursday night's . . . are especially for women." Tickets are priced at $3.50 for one program and $5.50 for both.

Each program consists of five films, ranging in running time from a minimum of one minute to a maximum of 50 minutes. The subjects range from quilting in Appalachia (Elizabeth Barrett's "Quilting Women,' a recent production of the estimable Appalshop is Whitesburg, Ky.), to lesbian reveries (Christine Mohanna's "Ninja," intriguingly described as "the haunting narrative of a lesbian who lives out her fantasy of becoming a samural warrior"). Tickets will be available at the door, or they may be purchased in advance at Lammas Women's Shop, Bread and Rosses or the Washington Area Women's Center. For further information call 546-7292.

A series on Chinese art history called "China: The Enduring Heritage" will be shown at Walter Johnson High School - in Bethesda on three consecutive Sundays from 3 to 5 p.m. beginning tomorrow. The programs consist of 13 films running 20 minutes each.The producer, Wang-Go Weng, is scheduled to appear at the opening program. Series tickets are priced at $6 with a $1 reduction for students and senior citizens. The comparable prices for single admissions are $2.50 $2. Walter Johnson High is located at 6400 Rock Spring Drive in Bethesda. Detailed information about the series, sponsored by an organization called The Organization of Chinese Americans, Inc., may be secured by calling Kung-Lee Wang at 634-1174 before 4:15 p.m.

The Boys Club of Greater Washington is sponsoring a benefit showing of "F.I.S.T." at the K-B Fine Arts on Tuesday at 8 p.m., the night before its theatrical opening at several area theaters. Ticket information is available at 462-4438.

A rare screening of Jean-Luc Godard's "Numero Deux," an example of his recent filmmaking obsessions, has been scheduled for the Holl Theater in the University of Maryland's Sudent Union on Sunday, April 30, at 3 p.m. Admission will be $2 at the door. Call 454-4987 for further information.