WASHINGTON -- Splitting 5-4, the Supreme Court imposed tight new constitutional limits yesterday on the creation of black-dominated election districts, endangering the political futures of thousands of officeholders, from Congress to school boards.
The lawmaker most immediately threatened -- second-term Rep. Cynthia A. McKinney -- sat solemnly in the courtroom and bowed her head as the court found her Georgia district to be an unconstitutional racial gerrymander.
That district was created in "a deliberate attempt" to bunch black populations together, the court said in a ruling that lambasted the Justice Department for using race too aggressively in pushing congressional redistricting in the South.
"Race was the predominant factor motivating the drawing of the 11th District," Justice Anthony M. Kennedy declared. That use of race, he said, was unjustified because it was solely an attempt to satisfy the Justice Department's insistence on "maximizing majority-black districts."
Accusing the department of "racial stereotyping," the court made clear that federal judges should not feel bound by the department's view on how race should be used in congressional redistricting.
The U.S. House seats most at risk appear to be those created after the 1990 census, when several states crafted districts that were based mainly on race, congressional and civil rights experts said yesterday. Some analysts said that as many as 12 House seats could be declared unconstitutional. Others said the ruling could threaten dozens more while jeopardizing thousands seats on city councils and school boards.
"There are thousands of redistricting plans in the South and throughout the country," said Laughlin McDonald, the top voting rights lawyer for the American Civil Liberties Union. "In light of [yesterday's] rulings, all of these plans are presumed to be unlawful."
In a related opinion yesterday, the justices refused to rule on the constitutionality of a black-controlled district in Louisiana. They said the voters who filed that challenge had no legal right to do so because they did not live in the district.
Opponents of the Louisiana district said they would be back in court soon with a new challenge.
The justices made clear that they would not leave the issue to the lower courts -- they agreed to rule next term on the constitutionality of black-dominated districts in North Carolina and Texas.
Yesterday's rulings came on the final day of the current term, a day on which the court's resurgent conservative majority had the votes to control all but one of the last round of opinions.
The most significant were the redistricting decisions, a pair of rulings that appeared to put in jeopardy many of the results of 30 years of government activity under the Voting Rights Act of 1965.
When that law was passed, the South had 72 black elected officials; today, the number is near 5,000 -- an increase that can be traced mainly to the strategy of creating single-member election districts, with majorities of black voters.
One of those who benefited from that tactic was Ms. McKinney, whose sprawling district runs from the Atlanta suburbs to precincts in coastal Savannah.
Yesterday, on the steps of the Lincoln Memorial, the congresswoman likened the court's ruling against her district to the Supreme Court's 1896 decision in Plessy vs. Ferguson, allowing racially segregated schools under a "separate but equal" theory.
"It is a sad note that almost 100 years after Plessy vs. Ferguson, this country and this Supreme Court have not been able to move beyond the question of the fundamental rights of this country's African-American population," she said at the site of Martin Luther King Jr.'s "I Have a Dream" speech in 1963.
The Supreme Court chose a test case involving her district to expand on its 1993 ruling that raised new questions about "racial gerrymandering" in congressional redistricting. In that decision, the court ruled that a black-dominated district probably would be unconstitutional if it was so odd in shape that it appeared to be crafted solely for racial reasons.
Yesterday, the court said challengers of districts that are based on race or ethnic background would not have to show that such a district was bizarre to try to get it overturned.
Challengers, the court said, may show by "direct evidence" that "race was the predominant factor motivating the legislature's decision to place a significant number of voters within or without a particular district."
If race was that important, according to the ruling, the district may be upheld only if the legislature had almost no choice but to use it, and then used race in the narrowest possible way. Race was a permissible factor, the court said, only if a legislature had a "compelling" public policy reason for using it.
But the court made clear that a Justice Department demand for adding more districts dominanted by minorities was not a valid reason. In Georgia, the court said, the department had insisted upon a third such district -- the one that elected Ms. McKinney -- even though the legislature preferred just two.
Justice Kennedy's opinion praised the Voting Rights Act, saying that it has been "of vital importance in eradicating invidious discrimination from the electoral process." But that goal "is neither assured nor well served by carving electorates into racial blocs," he said.
Justice Ruth Bader Ginsburg, one of the dissenters, said the ruling "renders redistricting perilous work for state legislatures."
Minority members of Congress were furious.
"We will not go back," said Rep. Eddie Bernice Johnson, a black Texas Democrat who could lose her district in south Dallas.
"We're devastated," said Rep. Eva Clayton, a North Carolina Democrat whose district is at stake in the next round of cases the Supreme Court will decide. "This will have an impact on many congressional and local seats, particularly in the South."
How many seats? No one was sure yesterday.
Charles E. Cook Jr., a former Democratic campaign official, said the ruling could force five or six states to redraw congressional maps.
"Until the new lines are drawn, we won't know for sure," said Mr. Cook, who publishes an independent political newsletter. "But there are a lot of Democrats who are privately saying this decision could really help them."
By redrawing congressional maps, particularly in the South, large blocks of black voters could be moved back into districts where Republicans now cling to slim vote majorities, according to Mr. Cook and other analysts and lawmakers.
"By and large, the decision is good for the Democratic Party, although it's not so good for African-American Democratic congressmen," said Stuart Rothenberg, an independent analyst who publishes the Rothenberg Report, a political journal.
"This thing cuts both ways," said Rep. Kweisi Mfume, a Baltimore Democrat and former chairman of the Congressional Black Caucus. "The question is whether this decision will throw out of kilter this new Republican majority in the South."
Benjamin Ginsberg, former general counsel for the Republican National Committee, said he thinks he knows the answer to that. With state legislatures in the South becoming increasingly Republican, he said he doubts they will redraw congressional maps to benefit the Democrats.
"I think the Supreme Court's decision is an employment act for lawyers and demographers," he said. "It will have little impact on the current political makeup of Congress."