WASHINGTON (AP) -- The Supreme Court is diving into a debate over school diversity that is as old as Reconstruction-era efforts to integrate blacks into the mainstream and as new as the 5:35 a.m. start time on some buses carrying students across town in Louisville, Ky.
At a time of rising de facto segregation in public schools, the high court is to hear arguments Monday on lawsuits by parents in Louisville and Seattle who are challenging policies that use race to help determine where children go to school.
The school policies are designed to keep schools from segregating along the same lines as neighborhoods.
Educators, civil rights advocates, politicians and parents -- not to mention students -- are watching for a potential watershed ruling on what value the nation should place on diversity in the classroom, and at what price.
The answer may hinge on the court's newest member, Justice Samuel Alito, who replaced Sandra Day O'Connor in January.
A year ago, O'Connor and her colleagues refused to hear a similar school diversity challenge from Massachusetts. After Alito's arrival, the court surprised many observers by agreeing to hear the appeals from Louisville and Seattle. Federal appeals courts had ruled in favor of both school systems.
The challenges could prove among the most significant K-12 desegregation cases since the landmark Brown v. Board of Education ruling in 1954 that banned racial segregation in public schools.
Civil rights advocates are not optimistic.
The new cases ''put on the table, in a very clear way, the question of how far society, how far government, should go in terms of trying to promote diversity in education in America,'' said Ellis Cose, the author of a study on affirmative action.
''The core issue of whether the government should be in the business of helping to promote diversity in some way in education is at the heart of all these cases,'' he said.
The Bush administration is siding with parents against the school districts, arguing the policies are an unconstitutional, albeit well-meaning, ''racial balancing'' without a compelling justification. ''A well-intentioned quota is still a quota,'' the administration said in a brief submitted on the Kentucky case.
Civil rights advocates say a ruling that bars schools from taking race into account would deal a devastating blow to the promotion of diverse schools.
If the court issues a sweeping ruling against using race, ''we will be witnessing a reversal of historic proportions,'' said Ted Shaw, president of the NAACP's Legal Defense and Educational Foundation.
''Race-neutral'' alternatives such as lotteries or socioeconomic sorting often end up segregating school populations again and hurting black students, according to Shaw's organization.
About 400 of the nation's 15,000 school districts are under court orders to desegregate. It is believed that hundreds more voluntarily take race into account; there are no firm figures.
The Leadership Conference on Civil Rights says banning the voluntary consideration of race in school assignments could result in an ''absurd'' situation in which districts are not allowed to promote the diversity they once were under order to achieve.
But to some parents, all of that is broad theory that does not compensate for denying kids the school of their choice or the one in their neighborhood.
Louisville parent Crystal Meredith, who is white, challenged a district policy that seeks to keep black enrollment between 15 percent and 50 percent of the population at most schools, while allowing some measure of school choice.
Meredith says the plan kept her son, Joshua McDonald, from attending a nearby elementary school. Instead, she says, he was bused 90 minutes away for two years, until she moved and her son got into his school of choice.
The result, says her legal brief, ''denigrates a 5-year-old's self-worth and self-esteem'' by color-coding him throughout his school years.
Not only white parents objected.
Deborah Stallworth, who is black, says she was unhappy when her young son initially was denied admittance to his neighborhood school. He was assigned to one across Louisville that would have required ''busing my baby halfway to Timbuktu,'' as she recalls it. Stallworth got the decision reversed.
Now 15, her son, Austin Johnson, is thriving at predominantly black Central High School, a magnet school barred by court order from taking race into account.
Stallworth says arguments that a diverse student body is necessary to teach children how to get along are nothing but ''foolishness,'' recalling her own years in segregated Louisville schools before court-ordered busing began.
''I don't have any problems getting along with anybody,'' she said. ''I have a good life.''
But Pat Todd, director of school assignment for the Jefferson County schools, said most parents value the diversity produced by the school assignment plan. Todd said 95 percent of families get their first or second choice of school and the average bus commute in the district is 45 minutes.
''The plan has prevented the resegregation that inevitably would result from the community's segregated housing patterns and that most likely would produce many schools that might be perceived as 'failing,''' the school district said in its brief to the high court.
To sisters Cassandra and Audreyanna Cosby, who are black, mixing students from around the county provides a valuable social education as well as an academic one.
''You get to check out different environments,'' said Cassandra, 16, a sophomore at Central High, the same school Austin Johnson attends. Audreyanna, 14, a freshman, said: ''You get to see how other people do it. ''If you stay in one school, in one neighborhood, you don't know what the other schools got.''
The Seattle plan let students pick among high schools while trying to maintain a 40-60 ratio of whites to nonwhites at each school. A racial ''tiebreaker'' helped to determine which students were admitted to popular schools that were ''oversubscribed.''
In 2000-2001, about 300 of 3,000 ninth-grade students were denied the school of their choice because of their race; the racial tiebreaker was discontinued after a group of parents sued.
''We teach our children in the Seattle public schools that people shouldn't be discriminated against,'' said Kathleen Brose, the president of the group that sued. ''Then when they get to ninth grade, we're judging them by the color of their skin.''
But a U.S. district judge in Seattle and the 9th U.S. Circuit Court of Appeals upheld Seattle's practice, finding a compelling interest in securing the benefits of diversity.
''We stand for all the school districts in this country that believe Brown v. Board of Education still applies,'' said school district lawyer Shannon McMinimee.
''Communities are still segregated, either by the history of racism in America or by current circumstances like the affordability of housing. This is about what a school board can do to remedy the effects of past segregation,'' McMinimee said.
Amy Stuart Wells, a sociology professor at Teachers College of Columbia University, said adults who attended racially diverse schools in their youth believe they are more open-minded and less fearful of other races than peers who went to segregated schools.
While racial tensions of the students' school years were challenging, Wells said, ''when you talk to them 20 years later they understand what it did for them. They understand how it helped them in a multiracial society and in a global society.''
The cases are Parents Involved in Community Schools v. Seattle School District No. 1, 05-908; and Meredith v. Jefferson County Board of Education, 05-915.
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Associated Press writers Gene Johnson in Seattle, Brett Barrouquere in Louisville and Mark Sherman in Washington contributed to this report.