The Supreme Court agreed yesterday to decide whether the First Amendment protects news organizations from being sued for revealing the identity of sources to whom they promised confidentiality.

The court said it will hear the case of a Minnesota political activist who sued two newspapers for unmasking him as the leaker of information damaging to an opposition candidate after giving assurances that his identity would remain secret.

The case, Cohen v. Cowles Media Co., has attracted widespread attention from press lawyers and journalists because it raises the issue of what duties reporters owe to sources whose anonymity they have guaranteed and whether such promises are legally enforceable.

In other action yesterday, the high court ruled unanimously in Groves v. Ring Screw Works that workers who are covered by union contracts have the right to go to court after grievance procedures fail, even when their contracts do not specify the right to file suit.

The justices also signaled their interest in resolving an important civil rights issue left undecided by their 1989 ruling in Patterson v. McLean Credit Union narrowing the reach of a post-Civil War rights law. The court asked the Justice Department for its views on whether the law -- which the court said in Patterson did not cover harassment on the job -- applies to racially based firings. The case is Brown Group Inc. v. Hicks.

In the confidential source case, the Minnesota Supreme Court threw out the breach-of-contract lawsuit by Dan Cohen, a longtime activist in the state Republican Party, against the state's two largest newspapers, the Minneapolis Star Tribune and the St. Paul Pioneer Press Dispatch.

Cohen, working during the 1982 gubernatorial race on behalf of Republican nominee Wheelock Whitney, contacted four reporters a week before the election. In exchange for a guarantee that his identity would not be revealed, he gave them court records showing that the Democratic-Farmer-Labor candidate for lieutenant governor, Marlene Johnson, had been convicted of shoplifting 12 years earlier.

The Associated Press honored the promise and used the story without identifying Cohen; a local television station did not run the story.

Editors at both papers decided that the origin of the attacks on Johnson was relevant to the reports. Over the objection of the reporters, they identified Cohen as the source of the information in articles published the next day. Cohen was immediately fired from his position at an advertising agency.

He sued the papers for breaking their promise of confidentiality, which Cohen argued was a legally binding contract, and won $700,000 at trial -- a verdict later cut by an appeals court to $200,000. In July, the Minnesota Supreme Court, voting 4 to 2, overturned the award, saying that constitutional protections for a free press outweigh the importance of enforcing promises to sources.

Describing the dealings between Cohen and the reporters as "a transaction fraught with moral ambiguity," the Minnesota court said reporters' promises to sources were an "ill fit" that imposed "an unwarranted legal rigidity on a special ethical relationship."

The state court analyzed the case under a legal theory known as "promissory estoppel," under which courts sometimes enforce promises that do not technically qualify as contracts. It said that free speech considerations in this case -- involving the "classic First Amendment context" of politics -- outweighed the state's interest in protecting promises of anonymity.

It said forcing newspapers to risk damages for promises made in such situations "chills political debate," but it left open the possibility that the balance might be different in other cases.

In a dissent, Justice Lawrence R. Yetka accused the majority of misusing the First Amendment to "carve out yet another special privilege" for the press.

He said it is "unconscionable" to let the press "hide behind the shield of confidentiality when it does not want to reveal the source of its information" and at the same time "violate confidentiality agreements with impunity when it decides that disclosing the source will help make its story more sensational and profitable."

Another dissenting justice, Glenn E. Kelley, warned that the ruling would have the effect of " 'drying up' potential sources of information on public matters."

In asking the high court to hear the case, Cohen's lawyer argued that the Constitution does not "allow the media to escape the consequence of violating promises." Lawyers for the two newspapers urged the court to let the state ruling stand, contending it was purely a matter of state law involving a highly unusual factual situation.