WASHINGTON — Supreme Court justices appeared reluctant Tuesday to expand protections of a landmark voting rights law in a case from North Carolina.

Until recently, civil rights advocates pressed lawmakers and courts to draw electoral districts with African-American majorities to help elect minority candidates.

But the creation of majority black districts across the South in the early 1990s that led to the election of more black Democrats also brought to office more white Republicans and fewer white Democrats.

So civil rights and Democratic leaders decided they would be better off with some districts in which African-Americans, though not a majority, still were numerous enough to determine the outcome of elections with the help of small numbers of like-minded white voters.

Three weeks before Election Day, the Supreme Court confronted a case that asks how small minority populations can be and still elect the candidates they want for local offices and Congress in areas where votes tend to fall along racial lines.

In the North Carolina case, the justices are being asked to extend a provision of the 1965 Voting Rights Act to protect districts in which, together, black and white Democrats can determine the outcome of elections. "They help to diminish the amount of racial polarization over time, so that eventually we won't need to be looking at race at all in drawing district lines," North Carolina Solicitor General Christopher G. Browning Jr. told the court in defense of the districts.

The court appeared divided in a familiar fashion. The more conservative justices sounded reluctant to expand legal protections to these districts, while their more liberal colleagues seemed more willing.

Justice Anthony Kennedy, so often the key to the outcome, appeared once again to hold the balance of power on the court.

And Kennedy appeared skeptical of the state's position. "What's the authority that says you must consider race in drawing the districts, assuming that you don't have an existing ... minority-majority district?" Kennedy asked.

Last year, the North Carolina Supreme Court struck down a state legislative district in which blacks made up only about 39 percent of the voting age population. The Voting Rights Act applies only to districts with a numerical majority of minority voters, the court said.

The Bush administration urged the U.S. high court to uphold the North Carolina ruling. "The problem is once you go below what is at least in principle a 50 percent line, it's not clear ... where one would ever stop," Justice Department lawyer Daryl Joseffer said.

Unmentioned Tuesday was the upcoming presidential election in which, win or lose, a black candidate is certain to garner the votes of tens of millions of whites.

The case is Bartlett v. Strickland, 07-689.