Washington ? What the Supreme Court says this year in its most significant ruling about race in a generation probably depends on just one or two of the court’s nine members.

Justices Sandra Day O’Connor and Anthony Kennedy, the court’s perennial swing voters, could write the demise of affirmative action as the nation knows it, or rewrite the rules for when race can be part of government decisions.

The historic affirmative action cases the court takes up today ask how and whether race can be a factor when public colleges and universities choose their students. More broadly, the cases ask wrenching legal and constitutional questions about equality, fairness, opportunity and history.

“It is very likely that it will be 5-4,” UCLA law professor Eugene Volokh said of the court’s eventual vote. “The question is, 5-4 which way?”

The University of Michigan and its law school give extra credit to minority applicants, making it more likely that a black, Hispanic or American Indian will edge out a white applicant who has similar test scores, grades or other attributes.

Three white students who challenged the Michigan policies frame their argument in simple terms: It is not fair for a minority to win a coveted place on campus just because he or she is a minority.

The university and dozens of supporters counter that a diverse student body is a worthy goal that benefits all students. Government, in this case a public-funded university, has what the Supreme Court has called a compelling interest in furthering that goal, the school argues.

The cases directly address only admissions at public, tax-supported institutions, but the court’s rationale is expected to have a wide ripple through private colleges and universities, other government decision-making and the business world.

Crowds gathering

In a measure of the issue’s importance, people began lining up a day early for scarce seats in the courtroom for today’s oral arguments, and hundreds of pro-affirmative action demonstrators were expected to gather outside the court this morning.

O’Connor, even more than her fellow swing voter Kennedy, is likely to listen closely to arguments about the practical effect of the university admissions plans, lawyers said.

“Who are they talking to? The answer is Justice O’Connor,” said Nathaniel Persily, a constitutional law professor at the University of Pennsylvania.

“Justice O’Connor has proved herself to be the swing vote on previous affirmative action cases and in other cases dealing with race-consciousness in government programs,” such as government contracting and legislative redistricting in the South, he said.

Both O’Connor and Kennedy are moderate conservatives named to the court in the 1980s by former President Reagan. They joined the court’s three-member conservative wing to form the majority in Bush v. Gore, the case that effectively settled the 2000 presidential election, and that same 5-4 lineup often prevails in some of the court’s most ideologically polarizing rulings.

The four more liberal justices typically score victories when O’Connor and Kennedy peel off, together or singly, and give their side a majority.

Lines are drawn

On affirmative action, the views of most of the justices are fairly clear.

Based on the justices’ writings and votes in past cases, many lawyers expect Chief Justice William H. Rehnquist and justices Antonin Scalia and Clarence Thomas to vote to strike down the Michigan programs as unconstitutional.

Likewise, Justices John Paul Stevens, David Souter, Ruth Bader Ginsburg and Stephen Breyer are expected to approve the program.

The justices have waded through more than 100 briefs filed in the case, most of them friend of the court filings supporting the notion of affirmative action if not its precise use at Michigan.

They will hear from lawyers for both sides, as well as from the Bush administration, which opposes the Michigan plans but did not call for an outright end to affirmative action.