Musindo Mwinyipembe, co-producer of a controversial film about racism in Britain, grew up in England without thinking about racism once.

It took a stint in America, a racially mixed marriage and a return to Britain as an adult to bring the message home.

"It was as if nobody else (but whites) existed on the island," she says in a finely modulated, British boarding-school accent. "Blacks were ignored. Or if they got any attention, it was strange. Someone in Parliament asked the question: 'What is their fertility count?' When I saw myself being discussed like this, I knew something was seriously wrong with those people."

How did she fail to learn about racism in Britian in the 1950s, a time when waves of West Indian, African, Indian and Pakistani migrant workers began raising British ire? When she herself had been brought there from Tanzania at the age of 6 for treatment of polio, and plunked down into an alien culture?

"I know it sounds odd," she replies. "But from the time I was 6 until I was 18, I lived in a convent boarding school (in London's Sussex district). Many of the students were children of the upper class.

"Occasionally someone would call me 'blackie,' but the other students would gather around me and tell me to ignore them."

Mwinyipembe, 34, was in Washington the other night screening "Blacks Britannica" at the Black Film Institute. She and her husband, David Koff, made the film, a tough indictment of British treatment of the Caribbean, African and Asian minorities, said to number almost 2 million, or about 3 percent of the British population.

Using no narration, the original film includes commentary and historical background almost exclusively from blacks, several of whom are Marxists. The producers say the firm points up the increasingly militant attitudes among blacks and Asians.

But the film has become a thorny issue for Boston's WGBH-TV, the PBS affliate that commissioned the documentary.

The film was altered (the station says "reorganized"; the producers say "censored" without their knowledge) before its initial showing in August of last year.

Lawyers were called in and are still trying to untangle the question of who owns the documentary - the filmmakers or the station that funded the film.

Thursday night at the screening, Mwinyipembe said WGBH had deleted material suggesting that British racism was conspiratorial, that interviews with Conservative party members Margaret Thatcher (now prime minister) and Enoch Powell set the tone for the expurgated version and that scenes of police target practice were edited out.

The editing, she contended, changed the focus of the film as it was expressed by the people who lived the experience. At a screening of the unedited version in London, she said, a British woman exclaimed, "This is incredible. My father came from Ireland in 1922, and this comes closer to the way he described the English than anything I've ever known."

"If WGBH had any quarrel with the film, they should've talked to us about it before the negative was cut," says the filmmaker, still speaking gently although her forehead became crowded with wrinkles. "Their quarrel was really with the way black people in Britain see themselves."

Though she narrated and assisted her husband in the production of "Black Man's Land," an excellent three-part documentary on Kenya, and served as assistant producer for Black Journal, a weekly PBS magazine show, Mwinyipembe says her work on "Black Britannica" marked a giant step in her growth as a filmmaker.

"After making the film, I started speaking out more," she explains. "I became less of a trusty aide and more of an equal working partner."

She began reappraising their roles in the home (they've lived in New York and London in recent years), in raising their 8-year-old son and 6-year-old daughter. She questioned, for instance, the effect it took her to prepare several meals for the week on Sunday so that she could be free for filmmaking during the week. And she made some changes.

Mwinyipembe, 5-foot-1, who walks with a limp because of her bout with polio, now says she'd like to make a film on black women's roles.

Until recently, most people did not know that Mwinyipembe and Koff, a Tanzanian woman and white American man, were husband and wife.

"We don't advertise it," she says. "We wanted to be independent. I suppose we didn't believe in the Western European idea of marriage - the royal merger of 'we'. Also, we haven't talked about it because some people would try to make a big thing of it." CAPTION: Picture, Musindo Mwinyipembe, by Ken Feil - The Washington Post