A divided Supreme Court yesterday dramatically reduced the power of federal courts to rewrite state and local election laws in voting rights cases.

The decision, a major defeat for blacks and other minorities fighting electoral schemes that exclude them from office, held that proof of the exclusion is not enough to warrant court action. They must also prove that the exclusion was intentional, the court said.

The justices oveturned one of the most sweeping court orders in recent civil rights history, in which U.S. District Court Judge Virgil Pittman restructured the entire Mobile, Ala., government largely because no black had won city office.

He ordered the city's at-large system of electing its commissioners, which he said caused the exclusion, changed to a single-member district or ward system.

Without proof that the at-large system was specifically designed to exclude blacks, the court ruled yesterday, Pittman's action amounted to guaranteeing blacks a seat on the commission.

The Constitution "does not entail the right to have Negro candidates elected," Justice Potter Stewart wrote for the four-man plurality. It "prohibits only purposefully discriminatory denial . . . of the freedom to vote . . ."

Six of the nine justices agreed to overturn Pittman's order, though only four agreed on the reasons. Justice Thurgood Marshall, the most bitter of three dissenters, said that the decision leaves "the politically powerless with nothing more than the right to cast meaningless ballots."

The court has already required proof of intent in employment discrimination and school desegregation cases. In voting cases similar to Mobile's, however, that proof is especially difficult to find.

Actions leading to the exclusion of minorities often occurred generations ago -- Mobile instituted its system in 1911, for example -- and relevant documents and testimony may no longer exist.

The four justices imposed especially rigorous standards for proof of discriminatory intent, downplaying the relevance of a history of discrimination cited by blacks in the case of Mobile, which is 35 percent black.

"Past discriminatioin cannot, in the manner of original sin, condemn governmental action that is not itself unlawful," Stewart wrote.

The decision takes on special significance because of the view among many civil rights activists that lawsuits such as Mobile's have been the most effective means towards black political power.

Beyond that, the decision may jeopardize expected challenges to reapportionment and redistricting plans across the country this year after the census.

The ruling does not apply to lawsuits brought under the one-man, one-vote principle of apportionment or to complaints alleging a direct denial of voting privileges protected by the Voting Rights Act.

The blacks in the Mobile case alleged, in effect, that there was an indirect denial of their voting rights under a system that allowed them to cast a ballot, but gave them no ability to win elections.

The four justices -- Stewart, Chief Justice Warren Burger, Justice Lewis Powell and Justice William Rehnquist -- suggested that the lower courts rendered their opinions out of confusion about previous Supreme Court decisions.

In the view of some lawyers, yersterday's split voting may cause more confusion. Justice Harry Blackmun agreed with the result but thought it proper only because Pittman's remedy was too extreme.

Justice John Paul Stevens, also agreeing with the result, felt that new standards of proof should be defined, standards the blacks in Mobile had not met.

Justice Byron White, one of the three dissenters, said that the old standards of proof were adequate and that the blacks had met them.

The other dissenters, Justice Willliam Brennan and Marhsall, argued that proof of intent was entirely unnecessary.

Following what has become a pattern, the court issued an opinion favorable to civil proponents yesterday to offset its unfavorable one.

By a vote of 6 to 3, the court upheld the constitutinality of the Voting Rights Act of 1965 in the face of a challenge from officials of Rome, Ga. Rome had changed its election system without obtaining clearance from the U.S. attorney general, as is required by the law.

It then challenged both the application of the act to cities, as opposed to states, and its constitutionality. Justice Marshall wrote the opinion in the Rome case and was joined by Burger, Brennan, White, Blackmun and Stevens. rPowell, Rehnquist and Stewart dissented.

In other decisions yesterday:

The court voted 5 to 4 to strengthen the right to sue for damages when government officials violate constitutional rights. Previously, lawsuits based on a constitutional violation could not be pursued if Congress had provided some other legal avenue for the violation.

Yesterday's case stemmed from the death of an immate in 1975 in a Terre Haute, Ind. federal prison. The prisoner's mother, Marie Green, sued federal prison officials for $2 million. Lower courts had barred her from collecting damages saying that her case was controlled not by the Constitution but by the Federal Tort Claims Act.

The court also held that workmen's compensation laws giving lesser benefits to widowers than to widows are discriminatory. The case, Wrengler vs. Druggists Mutal Insurance Co., stemmed from a Missouri requirement that the widower prove he was dependent on his wife's earnings before collecting death benefits under her workman's compensation coverage. No such requirement was imposed for widows.