ASHINGTON, June 26 — The Supreme Court endorsed a new approach to racial redistricting today by holding that when states draw new legislative boundaries they may consider overall minority influence in the political process, not just the number of minority voters in a given district.

The 5-to-4 ruling also endorsed a tactic Democrats employed in several states — including Georgia, Alabama, North Carolina and New Jersey — after the 2000 census when they sought to put substantial numbers of black voters in districts where they could shore up white Democrats.

Republicans fought them, seeking to concentrate black Democratic voters in fewer districts. They argued that districts with big black majorities were essential to comply with the Voting Rights Act.

The Voting Rights Act, passed in 1965, prohibited states from denying the vote to people on the basis of race or color. Literacy tests, which had been widely used to deny Southern blacks the vote, were banned. Southern states that sought to change any laws relating to voting, including those on registration hours and maps of legislative or Congressional districts, were required to clear them with the Justice Department or a federal court in Washington. In recent years, most litigation over the act has involved redistricting.

Though the Supreme Court never took that position, the Justice Department contended in the 1990 round of redistricting that any reduction in the percentage of minority voters in a district amounted to an impermissible "retrogression," or reduction, of minority voting rights. In states where that argument prevailed, more black candidates were elected, but Democrats lost seats overall because they lost reliable black Democrats from districts with white majorities.

Today's decision, written by Justice Sandra Day O'Connor, amounted to a refinement of the definition of retrogression, holding that a balancing of factors, not just the number of minority voters in a given district, was necessary to judge a plan.

While the decision turned on the vote of a single justice, there appeared to be broad agreement in both camps that the older standard — that districts had to have overwhelming black majorities to comply with the act — was outdated. If states could show that blacks had a serious chance of winning in districts where they were less than a big majority, most justices agreed, then reducing the size of the black majority in those districts could still be acceptable.

The case involved a redistricting plan from Georgia where the legislature had reduced the number of blacks in three state Senate districts, but made sure the black population of voting age in those districts did not fall below 50 percent. Georgia's attorney general had argued before the Supreme Court that although the changes may have slightly reduced the prospects of black voters electing a candidate of their choice, they increased the prospects of Democrats who hold positions favorable to blacks being elected.

Justice O'Connor, writing for the majority in the case, Georgia v. Ashcroft, said it was essential for courts to examine the overall impact of a districting plan, including the number of " `influence districts,' where minority voters may not be able to elect a candidate of choice but can play a substantial, if not decisive, role in the process."

"The state may choose," she wrote, "that it is better to risk having fewer minority representatives in order to achieve greater overall representation of a minority group by increasing the number of representatives sympathetic to the interests of minority voters."

Those dissenting from today's ruling, led by Justice David H. Souter, contended that the decision was so imprecise that it invited discriminatory redistricting efforts by lawmakers who did not have the interests of minority voters at heart. They argued that in the case before them the state failed to show that blacks' voting power would not be diminished. Justice Souter wrote that the decision meant "there will simply be greater opportunity to reduce minority voting strength in the guise of obtaining party advantage."

The majority did not say whether the plan Georgia Democrats pushed through in 1991 was lawful or not. Instead it told the District Court that had invalidated the plan on a 2-to-1 vote to re-examine the case and pay more attention to the views of minority lawmakers in the state who had endorsed the plan. The majority also said the appeals court should consider whether the new scheme might produce a Democratic majority in the state Senate and result in blacks' attaining committee chairmanships.

In addition, the court told the appeals panel to factor in whether reductions in African-American percentages in some districts were offset by gains in others. Whatever the lower court decides, the case is likely to come back to the Supreme Court in a few years for further definition.

Racial redistricting issues have traditionally divided the court. But Professor David T. Canon of the University of Wisconsin, a student of the issue, observed that one striking thing about today's opinion was that the same five justices who agreed on the ruling in 2000 that George W. Bush was president "were voting with the Democratic Party against the Bush administration. Race trumps party on this issue."

Republican Congressional leaders had no comment. But Representative Martin Frost, the Texas Democrat who has led his party's redistricting efforts, praised the decision, saying it agreed with the Democrats' view that minority voters could have more power if they could influence the results in many districts.

On one crucial point, Justice Souter and the rest of the minority agreed with the majority. "Reducing the number of majority-minority members within a state would not necessarily amount to retrogression," he wrote, "if a state can show that a new districting plan shifts from supermajority districts, in which candidates can elect their candidates of choice by their own voting power, to coalition districts, in which minorities are in fact shown to have similar opportunities when joined by predictably supportive nonminority voters." But he said the lower court was right in deciding that Georgia had not met the burden of showing such opportunities would result.