A refusal to hire former heroin addicts who are being treated with methadone violates neither their constitutional right to the equal protection of the laws nor the ban on racial discrimination in the Civil Rights Act of 1964, the Supreme Court ruled, 6 to 3, yesterday.

The court reversed the 2nd U.S. Circuit Court of Appeals in a case involving the New York City Transit Authority, which has a blanket policy barring employment to former heroin addicts.

A federal judge found that the policy, while not adopted with a discriminatory purpose, had a discriminatory impact. He relied on two statistics: blacks and Hispanics constitute 81 percent of the employes referred to the authority's medical consultant for suspected violation of the narcotics policy, and between 62 percent and 65 percent of all New Yorkers maintained on methadone.

He also ruled that the Constitution will not tolerate a blanket exclusion of all users from all jobs -- not just subway and bus operators but also car cleaners and track repairmen.

The appeals court affirmed on the constitutional ground without reaching the holding as to the Civil Rights Act.

"We do not condone this departure from [the] settled federal practice" of deciding a case on the law unless constitutional adjudication is unavoidable, Justice John Paul Stevens wrote in the opinion for the Supreme Court majority.

He went on to hold that the statistics relied upon by the District Court do not support the conclusion that the Civil Rights Act was violated by the authority policy. As for the guarantee of equal protection, Stevens said that the policy does not implicate the principle it protects.