ONE OF THE NATION'S strongest defenders of freedom of the press -- Supreme Court Justice William J. Brennan -- told off the nation's journalists last week. Speaking in Newark, he charged the press with engaging in unnecessarily vehement, unreasonable and unintelligent attacks on the Supreme Court. By doing so, he said, the press is destroying its credibility on issues vital to its future welfare and to the proper functioning of free government.

There are "hard words," as the justice said. They should have sent quivers through newspaper offices and broadcasting stations all over the country. For they came not from a disappointed politician or a judge who believes he has been badly treated by the press but from a friend on whose support, in judicial circles, the press has come to depend.

Justice Brennan cited -- by name -- newspapers that have based harsh criticism of specific decisions on "inaccurate reporting." He listed -- also by name -- newspapers and newsmen whose criticism he believes has been based on a failure to understand either what the court decided in a particular case or why it reached its decision. Even those, like us, who escaped specific rebuke felt the sting of his words.

His main point was that the press has been clinging to an old and revered concept of the First Amendment that more or less absolutely prohibits any interference with freedom of expression. The court, he argued, accepts that concept but has moved beyond it to use the First Amendment also to protect other things -- the structure of the communicative process through which citizens exercise their right of self-government. Questions arising under that second concept require the Supreme Court to balance the rights claimed by journalists against other social interests, a process in which it can engage without endangering the basic right of free expression.

This is a fascinating, and highly useful, analysis of what the court has been doing in recent years. Unlike most criticisms of the press, it provides a theory whose wisdom the press and the judges can debate without engaging in outrageous rhetoric. It leads inevitably, if you accept its validity, to the conclusion that the court has been wrongly attacked for failing to rule absolutely in favor of the press on every occasion. When a balancing process occurs, as it does under this theory, in matters like libel and the shielding of confidential information, other social interests can outweigh the claims of journalists.

Justice Brennan urges the news media to understand this distinction and to cut back the rhetoric when the court decides issues that are not fundamental to freedom of expression. He cites, quite rightly, the bitter criticism -- most of it uninformed and unthoughtful -- heaped on the court last spring for its most recent libel decision. That round of denunciations, he suggests, diminishing the impact of the justified criticism that resulted when the court later authorized secret criminal proceedings. Because sound commentary on the court's work has always had an important place in its future decisions, his suggestion raises the possibility that the press is systematically eliminating itself from a role it has long held. That is not a possibility to be dismissed lightly.