The Supreme Court yesterday reversed a controversial ruling holding virtually the entire construction contracting industry in Eastern Pennsylvania and Delaware responsible for the job discrimination practiced by a single union hiring hall.

In a 7-2 decision written by Justice William H. Rehnquist, the court said the fact that the businesses and trade associations may have acquiesced in the hiring hall bias was not enough to implicate them in it.

The decision overturned a sweeping affirmative action order in the case and extended a principle the court has applied whenever possible in all civil rights cases: Proof of intentional discrimination is required before courts may impose corrective orders.

Yesterday's decision prevented what industry lawyers feared could become a major new approach to civil rights law. But it did not directly affect the most frequently applied employment bias statute, Title VII of the Civil Rights Act of 1964.

Dissenting Justices Thurgood Marshall and William J. Brennan Jr. called the holding "extraordinarily naive," accusing the court of tolerating "cleverly masked" and subtle forms of discrimination where intent may be impossible to prove. It lets the employers "hide behind the veil of ignorance," they said.

The contractors case, General Building Contractors Association Inc. versus Pennsylvania et. al., involved an interpretation of one of the country's oldest civil rights laws, Section 1981 of the Reconstruction era Civil Rights Act of 1866, which guarantees blacks equal rights to "make and enforce contracts" and has been used since the mid-1960s to combat employment discrimination as a backup to Title VII.

In 1969, three people who are black, Raymond Williams, Willie McKay and Donald Murchison, used the law to bring a class action discrimination complaint against Local 542 of the International Union of Operating Engineers, four heavy contruction contractors associations, an apprenticeship program and 1,400 employers, which, under collective-bargaining agreements, drew workers from the operating engineers hiring hall.

A U.S. District Court in Philadephia found the union guilty of discrimination. Although the employers and the rest did not participate in it directly, the court held them responsible anyway under a theory of "vicarious liability" and ordered the imposition of hiring and training goals and a back pay award that has not been resolved. The U.S. Court of Appeals for the Third Circuit affirmed the lower court's ruling.

Rehnquist said that the lower courts should have required proof of intentional discrimination, as the court has mandated in busing cases and voting rights cases under the Fourteenth Amendment.

Without that proof, there can be no liability, Rehnquist said. The "vicarious liability" theory, making the employers guilty for the acts of the union, did not apply because the union is not an "agent" of the employer or part of a "joint enterprise" with it, and the employer has no legal obligation to see that discrimination does not occur in the union, he said.

Rehnquist said the lower court exceeded its powers in imposing the order.

Justice Sandra Day O'Connor, joined by Justice Harry A. Blackmun, agreed with the ruling but wrote separate concurrences. Justice John Paul Stevens agreed with some parts but said he believed the law at issue was never meant to apply to employment discrimination cases.