By a 5 to 4 vote, the Supreme Court yesterday limited the power of the Justice Department to block proposed redistricting changes for local and state elections that might dilute the voting power of blacks and other racial minorities. Dissenting justices said the decision reverses a quarter-century of federal policy and ignores the effects of lingering segregation in some parts of the country.

The court said that the Justice Department cannot veto a proposed voting plan unless it puts blacks in a worse position than they were before.

The law in question, Justice Antonin Scalia wrote for the majority, was intended to prevent "backsliding." He said the dissenting justices' view, giving the federal government broader authority to intervene in local affairs, would "exacerbate the substantial federalism costs that the preclearance procedure already exacts."

At issue in the difficult case that the justices considered over two different terms was a provision of the 1965 Voting Rights Act that requires certain states and localities with a history of discrimination to get permission from the Justice Department before adopting a redistricting plan that affects voting rights.

The question was whether the provision allows Justice to reject a plan only if it leaves minorities worse off. Government lawyers argued that Justice should be able to veto a redistricting proposal based on the broader grounds that it has a discriminatory purpose, for example, to dilute African American voting strength.

The Justice Department had objected to the Bossier Parish (La.) School Board's plan giving all 12 voting districts white majorities, even though about 20 percent of the population is black. Affirming lower court rejection of the challenge, Scalia noted yesterday that the government has an alternative in a separate section of the act to challenge discriminatory voting rules already in place.

Dissenting justices said the majority too narrowly interpreted voting rights. Justice David H. Souter also observed: "The evidence in these very cases shows that the Bossier Parish School Board acted with intent to dilute the black vote . . . exactly the sort of relentless bad faith on the part of majority-white voters in covered jurisdictions that led to the enactment of" this part of the Voting Rights Act. The other dissenters in Reno v. Bossier Parish School Board were Justices John Paul Stevens, Ruth Bader Ginsburg and Stephen G. Breyer.