From behind their loftly mahogany bench, the justices of the nation's highest court have been assailing the First Amendment protections that safeguard individual liberties. The Supreme Court, clearly, places police powers above individual rights.

The decisions appear to be directed, in particular, at disrupting the city editor, investigative reporter and dissenting pamphleteer from acting as a watchdog on the power centers of society. First off, the Court sought to strip away the confidentially of news sources. Then the Court ruled that police, if they could find a friendly judge to issue a warrant, could rummage through the confidential files of a news office.

Those are dangerous steps toward putting the press under the control of government and blotting out all sources of information that compete with the official version. It could give the government security apparatus the power to stifle one of the most valuable but endangered species in American life - the informer.

There is a limit to what can be dredged up from interviewing malefactors and miscreants and studying such records as are available to the public. The principals rarely admit to wrong-doing, and the pertinent documents are either classified, falsified or strangely absent from the files.

Moreover, the reporter is hobbled by self-imposed limitations. Unlike the governments, the newsman has ethics that prevent him from wiretapping, burglarizing files, intercepting mail, buying information or planting paid spies.

There are legitimate ways by which he can develop sources and pursue leads. But when he reaches the place where the trail vanishes, he is lost unless some unknown insider comes forward with the missing clues. We have never found anything unethical in trying to tempt the insider to come out into the cold.

We have been cultivating informers for years; we know something about the psychology of one who has a dark secret and is teetering on the awful brink of disclosing it. His motive may be noble or base or just human; he may seek to protect the public from fraud, to advance a good cause, to discredit a rival or to avenge a personal grievance. To reporters, the motive should be secondary, except as it bears upon the validity of the information.

The informer is often a stranger to the glare of publicity and is full of doubt and fear. He usually does not know the news business. He does not know just whom to go to or whether his disclosure will be deemed newsworthy.

Maybe, he fears, they will just yawn or even laugh at him for trying to peddle such trival stuff, and he will have exposed himself for nothing. Most of the time, the informer wants to stay hidden. Exposure will cost him his livelihood and lay him open to the most depressing harassment. For our society has not yet outgrown the hoodlum ethos, which honors the man who covers up his boss's crime above the employee who exposes it.

Can the informer trust stangers to protect his anonymity? He knows vaguely that above the typical reporter are editors, lawyers, publishers - perhaps with advertisers to protect - any one of whom can kill the story after he has exposed himself or his cause to a widening circle.

And so for weeks he hangs immobilized between visions of derring-do and nightmares of retribution. Most of the time he never comes forward; and even when he does, he may turn back. We have had informants before us who, in the midst of their stories, have begun, to jabber, broken out in sweat and edged for the door.

We like to keep a light burning in the window for the storm-tossed informer. We signal to him from afar by championing his causes, by regularly printing exposes akin to his, by being accessible to the hushed voices on the phone, by periodically making public pledges to go to jail rather than reveal a source.

But the Supreme Court is now trying to shipwreck the wayfarer before he reaches our port. THe eminent jurists will find little justification for this in the nation's founding documents. On the contrary, the founders wanted a free press that would provide the people with a rival account of reality, a measure by which to judge the efficacy of rulers, an unauthorized stimulus to action or resistance.

Finally, there is the personal attrition to consider. To any muckraker of mature years, with average sensitivities, and emotions ad depletable as the next fellow's, the assaults of government begin to take their toll. Long ago he convinced himself that good will overcome evil if the actors are seen and the facts known.

He has invested his life in the proposition that pollution must be seen and smelled to be combatted, that corruption hidden is corruption heightened, that our institutions are still vital enough so that scandal will bring not demoralizations but reform. Still, he must always fight back insidious doubts.

In the end, he stays in the fight against those who would erode the First Amendment - whether they are crooked sheriffs trying to suppress local scandals or appeals judges ruling that Victor Marchetti's book about the CIA must be stripped of 168 sections the CIA doesn't like, or Supreme Court justices legitimizing police raids on news offices.

Together they constitute a Sixth Column that mortally endangers the one American freedom that is the bedrock of all the others - freedom to criticize. And they've got to be stopped.