WASHINGTON – Civil rights advocates listened glumly Monday as the Supreme Court confronted anew the divisive issue of race in education, this time in public school plans that take account of a student’s race to promote diversity.

The challenge for any lawyer hoping to win at the high court is to get to five – the number of votes needed among the nine justices. It was hard Monday to find five who appeared inclined to sign off on plans used in Louisville, Ky., and Seattle to keep schools from segregating along the same lines as neighborhoods.

“It’s even more difficult to win these cases now, and it was never easy,” said Theodore Shaw, director counsel of the NAACP Legal Defense and Education Fund.

Justice Anthony Kennedy, the court’s swing vote since the retirement of Justice Sandra Day O’Connor, showed no indication he would side with the court’s liberals to form a majority in support of the school integration plans.

Kennedy joined his conservative colleagues in indicating that the programs may run afoul of the Constitution.

Three years ago, a 5-4 ruling upheld the limited consideration of race in college admissions to attain a diverse student body.

A decision against the school districts could imperil similar plans in hundreds of districts nationwide and leave public school systems with a limited arsenal to maintain racial diversity. A ruling is expected by next summer.

In Monday’s cases, parents sued after their children were denied admission to the schools they preferred because of their race. The school policies in contention were upheld by federal appeals courts and are designed to keep schools from segregating along the same lines as neighborhoods.

School districts court trouble by “characterizing each student by the color of his or her skin,” Kennedy said during the argument over the Seattle case. “It seems to me that should be allowed, if it’s ever allowed, as a measure of last resort.”

Lawyers for the parents and the Bush administration said the plans violate the Equal Protection Clause of the 14th Amendment, enacted after the Civil War as part of the effort to remedy the effects of slavery.

The issue presents a unique challenge to Louisville’s schools, which spent 25 years under a court order to eliminate the effects of state-sponsored segregation. The Jefferson County, Ky., school board, which encompasses Louisville, decided to keep much of the court-ordered plan in place to prevent schools from re-segregating.

“What’s constitutionally required one day is constitutionally prohibited the next day? That’s very odd,” Justice Ruth Bader Ginsburg said, sentiments shared by her three liberal colleagues.

In a reversal of sorts, the court’s liberals spoke for local control of education policy.

Francis Mellen Jr., representing the Louisville schools, called the plan a success story that enjoys broad community support, including among parents of white and black students. Joshua McDonald, the child whose situation as a kindergarten student led to the lawsuit, was admitted to his school of choice beginning in the second grade.

Still, Kennedy wanted to know whether a school system that succeeds in freeing itself from court supervision can use a student’s skin color as a basis for assignment.

“We’ve never said that. That takes us on a very perilous course,” he said.

Chief Justice John Roberts and Justices Samuel Alito and Antonin Scalia also expressed concern about the school plans. Justice Clarence Thomas asked no questions, but he has consistently voted against racial preference plans.

Scalia derided the school systems’ policies as a “whatever it takes” approach that improperly classifies people on the basis of race.

Outside the court, affirmative action supporters bearing “Fight For Equality” placards marched on the sidewalk in a brisk wind.

Demonstrators chanted “Equal education, not segregation” and “We won’t go to the back of the bus, integration is a must.” Among the crowd were representatives of the National Organization for Women, the NAACP and students from Howard University.

Though outnumbered, there were some in the crowd from the other side.

“Regardless of how well-motivated, allowing the state to engineer racial mixing only creates racial stereotypes and increases racial tension,” said Terry Pell, president of the Center for Individual Rights, a public interest law firm. “The court needs to put an end to state-mandated tinkering with race.”