"Separate But Equal," ABC's two-part miniseries about th Supreme Court's landmark school desegregation decision, is itself almost landmark television in two respects. One is the performance of Sidney Poitier as Thurgood Marshall, the NAACP lawyer and future Supreme Court justice who argued one of the cases that became known as Brown vs. Board of Education. Poitier's acting style may be too big-screen rococo for some television tastes. But its moments of high-intensity grandeur make it one of the performances of the television year.

The other is that "Separate But Equal" is television's first major docudrama in more than a decade to deal with the real contributions of blacks to the moral and intellectual life of America.

The only other one that showed blacks shaping America on their own -- without a guiding white hand or two -- was "King," the 1978 miniseries about the Rev. Martin Luther King.

This doesn't mean that "Separate But Equal" is great entertainment television. Some viewers are likely to find tonight's first installment (9 p.m. on WJZ-TV, Channel 13) slow going. But the film's enlightened treatment of blacks and their impact on American life makes it mighty important -- one of the most important prime-time, entertainment television events of the season.

For those not familiar with real-life events leading up to Brown vs. Board of Education, here is some background.

In the early 1950s, segregated schools were legal. The Supreme Court had repeatedly upheld the right of states to segregate schools as long as the facilities were equal. Thus, the term "separate but equal."

But, also in the early '50s, the National Association for the Advancement of Colored People took on five cases challenging the doctrine. The cases, collectively known as Brown vs. Board of Education, culminated in the 1954 ruling that desegregated schools. Tonight's film starts out with one of the five, in South Carolina's Clarendon County.

The film's point of view and sharply honed social vision are stated during the opening, with a crystallized image of great eloquence.

The camera shows us a long shot of a black child walking along a dirt road. A big yellow school bus comes rolling along, passes the child and leaves him in a cloud of dust. The child, who never looked up at the bus, literally disappears as a second bus comes lumbering up the road and rolls past. The camera shifts from that long shot of the road to a window in a ramshackle schoolhouse nearby, where a black minister watches the scene with a look of profound sorrow.

This is what Part 1 is about -- that child not being able to get on a school bus in South Carolina in 1950. Just as the bus leaves the child behind, so does society.

The white students had 33 buses. The black minister wanted one bus for his students. When he could not get it from the school superintendent, the NAACP, in the person of Marshall, went to court on his behalf.

There are a whole bunch of good stories jockeying for position in the first couple of hours tonight. There is the one of the boy and his father and mother. The father lost his job when he signed the desegregation lawsuit. The mother and father had to leave South Carolina because of Klan reprisals. There were reprisals against the minister, too.

But it is Marshall's story and the courtroom battle between him and John W. Davis (Burt Lancaster), a famous attorney and Democratic candidate for president in 1924, that the narrative gravitates toward. By the end of tonight, the film is nearly all jTC theirs. Only the ethical odyssey of Chief Justice Earl Warren (Richard Kiley) while hearing the case will rival Marshall's story.

That's where the work of Poitier becomes all-engrossing. It's partly the acting, partly the persona.

Poitier has not done television since 1955. He is a movie star, albeit from earlier days. He is most closely associated with the early and mid-1960s ( "Lilies of the Field," "A Raisin in the Sun," "In the Heat of the Night" and "Guess Who's Coming to Dinner?"), times of great striving in the civil rights realm. He brings that aura of righteousness to the screen with him.

And, then, there is the performance itself. He plays Marshall as a relatively simple man -- beset by many problems and a few failures in his everyday life -- until he is in a courtroom.

Then, as if trying to show Marshall literally being lifted up by the majesty of the law, Poitier expands him into this regal character of Shakespearean stature and great moral authority.

And isn't that the way it really is? We rise to our moments of greatness. No one maintains that level every day. That is the smartest of many smart acting choices Poitier makes.

But the portrayal leads to the larger issue of how blacks of historical import are treated in "Separate But Equal." One of the really encouraging things about this film is that its central character is not an entertainer, like Josephine Baker, or an athlete, like Jackie Robinson; America is comfortable recognizing black entertainers and athletes.

This is about a black lawyer. It celebrates education -- Howard University Law School. It celebrates the intellect. Part of the story depicts the brain trust of NAACP lawyers and professors working on the case. It celebrates hard work -- all-nighters of legal research. It celebrates social conscience.

And it is about black men and women not only changing America, but in some ways, saving America from the downward spiral and certain death of its apartheid ways in the 1950s.

Outside of "King," with Paul Winfield playing the civil rights leader, no other commercial network production in the last 25 or so years (the time docudrama has been an entertainment formula) has seen fit to give black heroes such treatment.

Still, it is docudrama and therefore prey to the sins of that troubling blend of fact and fiction. There is a disclaimer at the start of the film from writer and producer George Stevens Jr. stating that the movie "is a dramatization based on interviews and accounts of the time, and contains created scenes and dialogue." Translation: As for historical accuracy, it is strictly buyer beware.

And because this is prime-time entertainment television, we need to remind ourselves as we watch that our history is being shaped to entertainment purposes.

That means events tend to be presented as being more dramatic than they may really have been. It also means some portrayals and some issues are made to seem more black and white than they may have been.

One other point: Stevens is white. Abby Mann, who wrote and produced "King," is white. They both did work that they can be proud of.

But it will be a landmark day of true celebration for the television industry when black writers and producers have the chance to tell the stories of heroes like Thurgood Marshall and the other men and women who sacrificed so much to desegregate America's schools and save the nation from its horrible sin of denying people the chance to learn.