Three major corporations seeking to prevent disclosure of equal employment information they file with the government won an important victory yesterday in the Supreme Court.

The court refused a government request to review a ruling that limits the discretion of federal agencies to grant requests under the Freedom of Information Act (FOIA) for data submitted by private parties.

The action was a surprise because the court usually grants petitions by the Solicitor General to review decisions in important cases.

The ruling is effective only in the Fourth U.S. Circuit - Maryland, North Carolina, South Carolina, Virginia and West Virginia. But dozens of other so-called "reverse" FOIA cases are pending elsewhere and may produce contrary rulings in other circuits likely will try to resolve the conflict If this happens, the Supreme Court and set a policy applicable throughout the country.

Yesterday's action developed from lawsuits brought by Westinghouse Electric, General Motors and United States Steel corps.

As a condition of doing business with the government, contractors are required by a White House executive order to treat all employees equally, without regard to factors such as race and sex, and to take affirmative action to eliminate discrimatory practices.

Labor Department regulations implement the order by requiring each contractor doing annual business of $50,000 or more with the government to file an annual report on employment of minorities and women and to make available the firm's affirmative action plan.

In the information law, Congress expressed its intent to afford "the fullest possible disclosure." To implement this intent, the regulations require that the report and the plan be available for inspection and copying to "any person," except for exemptions provided in the FOIA.

A group called Concerned Workers in East Pittsburgh, Pa., and the Legal Aid Society of Alameda County, Calif., asked the Defense Supply Agency (DSA) for data on Westinghouse and its Fraser & Johnston Co. subsidiary. The National Organization for Women (NOW), the Consumer Federation of America, the Gary, Ind., Commission for Human Relations, and the Urban League of Youngstown, Ohio, sought data filed by GM and U.S. Steel.

The companies resisted, contending that their reports contained confidential proprietary information that, if released, would adversely affect their business interests. When the DSA business interests. When the DSA overruled them, the firms sued, won in trial courts, and were affirmed by the Fourth U.S. Circuit Court of Appeals.

The appellate court relied on an exemption in the FOIA for trade secrets and privileged or confidential commercial or financial information and on another law prohibiting federal crets.

Similar reasons for nondisclosure were cited in the 78 "reverse" FOIA suits filed last year and by the Prudential, Metropolitan Life and John Hancock Mutual Life Insurance Cos. in a suit lost to the Washington, D.C., chapter of NOW in District Court here. Although the firms' appeal is pending in the Court of Appeals, they filed an unusual petition to the Supreme Court for review. Yesterday, the high court turned them down.

In unsuccessfully seeking review of the decision in the Westinghouse, GM and U.S. Steel case, the Justice Department said that ruling reflected "a misunderstanding" of what Congress termed the "dominant objective" of the FOIA: "the fullest responsible disclosure."

Lawyers for U.S. Steel said that tens of thousands of government contractors who file "an endless array" of materials with the government have stakes in the FOIA regulations. Ten makers of television sets, for example, have filed four separate suits to try to stop the Consumer Product Safety Commission from releasing data on accidents caused by color TVs.