The Supreme Court ruled 8 to 0 yesterday that judges in school desegregation cases must tailor remedies to fit the constitutional violations.

The decision fully adopts the position of the Justice Department in both the Ford and Carter administrations.

The court acted in a case from Dayton, Ohio, where, Justice William H. Rehnquist wrote in the opinion for the court, "mandatory segregation by law of the races in the schools has long since ceased."

The duty of federal trial and appellate judges in such cases is to determine if a school board intended to or did discriminate against minority pupils, teachers or staff, Rehnquist said.

Then, he wrote, they should measure the "incremental segregation effect" the violations had on, say, the racial distribution of the school population against what that distribution would have been had there been no violations.

"The remedy must be designed to redress that difference and only if there has been a systemwide impact may there be a systemwide remedy," Rehnquist said.

Justice William J. Brennan Jr. subscribed only to the judgment, although he agreed that the violations actually found by a U.S. District Court "were not sufficient to justify the remedy imposed." Justice Thurgood Marshall did not participate in the case.

The Dayton case has been in the courts for five years. The core problem has been to remedy Board of Education actions that denied the constitutional guarantee of equal protection of the laws in a northern city where state law did not mandate a dual school system.

After rejecting two less sweeping orders, the Sixth U.S. Circuit Court of Appeals approved a plan under which each of the city's 66 schools would be between 33 per cent and 63 per cent black - a variation of no more than 15 per cent, either way, from the 48 per cent black share of Dayton's population.

Making the plan effective would require regular and permanent busing of about 15,000 students and a variety of other desegregation techniques.

Yesterday, Rehnquist agreed with the lower courts that the school board had committed constitutional violations, but they said they did not "suffice to justify the remedy imposed."

The apellate court upheld a finding by the trial judge that the board had committed a "cumulative violation" consisting mainly of racially imbalanced schools and optional attendance zones. But that "cumulative liolation," even if reviewed in the worst light, [WORD ILLEGIBLE] not license the appeals court to impose a systemwide remedy, Rehnquist said.

"There had been no showing that such a remedy was necessary to 'climinate all vestiges of the state-imposed school segregation,'" he continued.

Rehnquist emphasized a Justice Department position that the Constitution is not violated merely because schools are predominantly black or predominantly white. But, he wrote, "the Court of Appeals appears to have viewed the present structure of the Dayton school system as a sort of 'fruit of the poisonous tree' . . ."

He acknowledged that the plan has been in effect in the school year now ending "without creating serious problems," and should remain in effect in the coming year, subject to changes ordered as a result of returning the case to the lower courts for new proceedings.

The court also acted in school cases from Detroit, Hazelwood, Mo., and the nearby city of St. Louis.

In the Detroit case, the court previously had ruled that an interdistrict remedy involving the suburbs exceeded the violation found in the city school system and sent the case back for new proceedings.

A federal judge then formulated a new desegregation plan, including compensatory or remedial reading, testing and counseling programs for children victimized by past segregation. He ordered the Detroit School Board and the State of Michigan to share the costs.

In a unanimous decision yesterday, the court upheld the plan. It is "aptly tailored" to fit the condition that offends the Constitution, Chief Justice Warren E. Burger wrote in the opinion for the court. He noted that disadvantages such as speech habits reflecting cultural isolation "do not vanish" simply from a move to a desegregated school. "The root condition . . . must be treated directly by special training at the hands of teachers prepared for that task," he said.

In the Hazelwood case, the court voted 8 to 1 to nullify and send back an English U.S. Circuit Court of Appeals ruling that the St. Louis County school district had been shown by statistics to have discriminated in hiring against black teachers. Justice Potter Stewart wrote that the appeals court erred in disregarding data on teacher hiring after. Hazelwood became subject to the civil rights act in 1972.

In the St. Louis case, the court let stand a ruling that six black pupils and the local branch of the NAACP had a right to challenge a desegregation consent decree accepted by the city school board in December, 1975.