CZECH DIRECTOR Milos Forman will introduce the American premiere of "Why Havel?" Tuesday at the Air and Space Museum. Vojtech Jasny, who directed the 1990 documentary about Czech leader and playwright Vaclav Havel, and producer Rock Demers, will alsoattend. It screens at 6:30 in Air and Space's Langley Theater. Admission, which includes a reception, is $26. Call 202/357-3030 for reservations.

ARTISTS and spouses Diego Rivera and Frida Kahlo are the subjects of both the 1984 drama "Frida" and Mary Lance and Eric Breitbart's 1989 documentary "Diego Rivera: I Paint What I See." The films screen at the Biograph this weekend. The theater's artist series continues Sunday through Tuesday with "Imago: Meret Oppenheim," a 1989 documentary by Pamela Robertson-Pearce and Anselm Spoerri about the Swiss surrealist. "Imago" is shown with David and Albert Maysles's 1978 "Christo: Running Fence," about the artist who creates large-scale drape-like constructions.

JACK STEVENSON, editor and publisher of Pandemonium Magazine and collector of weird movies, will present "Exploitation and Beyond," a selection of "rare, shocking and trashy films," including a medical training movie that "may be the goriest film ever made." Admission for the show (at 8 Monday at d.c. space, 443 Seventh St. NW) is $3. For more information, 202/387-0195.