The National Labor Relations Board has handed unions a powerful new tool for rooting out job discrimination.

In a 3-to-1 decision, the board ruled that employers can no longer deny unions access to detailed information about treatment of women and minorities needed for negotiating and servicing contracts.

Unions have a duty to "insure that discriminatory practices are not established or continued," and hence are entitled to information relating to possible job bias, the board held in a case brought by the International Union of Electrical Workers against Westinghouse Electric Corp.

The board held that Westinghouse acted improperly in refusing to give the union breakdowns by race and sex of statistics relating to wages, job classifications, seniority, hiring, promotions and discrimination complaints filed against the company.

Such information must be given to a union even if, as Westinghouse alleged in this case, the union intends to use the information in a lawsuit. As long as the information is relevant to collective bargaining, the union has a right to it, the board said.

"If information is relevant to collective bargaining, it loses neither its relevance nor its availability merely because a union additionally might or intends to use it to attempt to enforce statutory and contractual rights before an arbitrator, the board or the court," the board said.

In a separate case involving the IUE and the East Dayton Tool and Die Co., the board also held that - in that particular case - the union was entitled to statistics on the race and sex of job applicants as well as those already in the work force.

In a sharply worded dissent in the Westinghouse case board member Betty Southard Murphy accused her colleagues of reaching a "shocking result" in creating "an affirmative duty for unions to become agents of the EEOC [Equal Employment Opportunity Commission] with respect to ferreting out employment practices - regardless of the absence of any complaints by unit members, any grievances or even any suspicious."

She predicted that unions may wind up being held liable for unilateral discrimination by employers if they do not seek the information available to them. As a result of the decision, she said, "unions will find themselves burdened with a responsibility which they cannot reasonably or financialy be expected to fulfill."

The board majority did not address itself to that point specifically. At one point it noted, however, that it already held unions responsible for representing the interests of minorities and found them guilty of unfair labor practices when they refused to process grievances against alleged discrimination.

IUE general counsel Winn Newman said he interpreted the ruling to apply only to unions like the IUE that were seeking the information, rather than as an obligation for all unions to seek it out.

Although the NLRB decided the case Tuesday it was not scheduled to be announced until Monday. However, copies were released to both sides and made public by the IUE, which hailed the decision as a "landmark judgement . . . cutting new ground in union-management relations."