Haile Gerima's "Bush Momma," showing tonight at 7:30 at the Miya Gallery, is not a slick film, nor even smooth. It is too long. The sound is harsh and often garbled. The story line is sometimes confusing, sometimes overstated.

But "Bush Momma" is a picture that must be seen. The chronicle of a black woman in the Los Angeles Watts area who is driven to discover her identity and pride, this film crackles with energy. Fury shakes the very frame.

The opening shots are actual foot age of the filmmaker ketting the treatment by L.A. cops - the pistol at the throat, the Clint Eastwood two-handed target stance - all because he went for his filming permit in his back pocket. At their request, went for his filming permit in his back pocket. At their request.

The rest is fiction, done with a grainy, jerky verve that brings to mind Rossellini's great crypto-documentary "Open City," mostly with non-actors and some improvised dialogue. Whatever its faults, "Bush Mamma," which Gerima calls "the nightmare of me," is real. It deals in realities observed by an Ethiopian who studied film at UCLA and now is at Howard University teaching film.

As Gerald Scott, president of the sponsoring Compard To What? Inc., noted, these are not just the realities of Watts but the conditions that black people live with in many, many cities.

Following its strong opening, this "Alternative Film Festival" will present seven more films - free - mostly about and by American blacks. All will be shown at the Miya Gallery, 720 11th St. NW (347-6076), at 7:30 and if warranted a later hour as well.

The gallery, incidentally, is about 10 months old, the same age as its name-sake, Miya Gray, daughter of owner Vernard Gray. It specializes in the work of local black artists.

The rest of the festival:

Feb. 10, "Attica," Cinda Firestone's withering documentary about the prison riot. The filmmaker will speak afterward.

Feb. 24, "Story of a Three-Day Pass," the first film by Melvin Van Peebles.

March 10, "No Vietnamese Ever Called Me Nigger." Created by an amateur, David Loeb Weiss, the picture features an interview with Terry Whitmore, a decorated black GI who walked off the battle field in revulsion and fled to Sweden. It won the documentary award at Mannheim. Weiss will speak.

March 24, "The Education of Sonny carson" by Michael Campus: growing up black in Philadelphia.

April 7, "Finally Got the News," Steward Bird's documentary on working conditions in Detroit, accompanied by a short study of the assembly line, "Work," by Fred Wardenburg, Bird will be present.

April 21, "Lucia," the rarely seen masterpiece of revolutionary Cuban cinema, depicting three revolutions in that country as they affected the lives of three women.

May 5, the festival will end with Gerima's "Harvest 3000," relating the class struggle in Ethiopiawith the modern ghetto.