THE CIA'S vehement attack on the American Broadcasting Company is both peculiar and, as a precedent, disquieting. In news programs last September ABC reported that the CIA had proposed to assassinate a Honolulu financial figure named Ronald Rewald. The CIA denied it repeatedly and, last Wednesday, ABC acknowledged on the air that it could not substantiate the claim. On the same day, the CIA went to the Federal Communications Commission with a legal complaint charging that ABC, in a "deliberate distortion," had engaged in a "personal attack upon the character and integrity of the CIA, for which the agency is entitled to relief."

What kind of relief does the CIA have in mind? It wants the FCC to conduct an inquiry, to make its own findings, and to take those findings into account when it considers renewing the licenses of ABC's television stations. That has an ominous ring to it. One agency of the federal government is asking another agency of the same government to contemplate stripping a company of some of its most valuable assets, to punish it for defaming the government. But if the First Amendment means anything, it means that the government cannot legally penalize anybody for defaming it.

Mr. Rewald's company in Honolulu was involved with the CIA, although the nature of the relationship is not precisely clear. It's now bankrupt, and Mr. Rewald himself is under indictment for fraud. To pursue the matter further is not easy since, at the request of the CIA, the federal court has sealed the records in the case. But, in the course of following the news story, ABC interviewed a man named Scott Barnes who described, on the air, a discussion in which a CIA contact suggested killing Mr. Rewald. At the time that it put him on the air, the network had a sworn affidavit from Mr. Barnes. But, pressed by the CIA, it went back to him for further corroboration and, failing to get it, pulled back from that charge.

What recourse does a government agency have against people whose accusations, it feels, have injured it? The government has no power whatever to punish citizens, from large corporations to private individuals, for the exercise of free speech. A government agency has every right to do what the CIA did at first -- to deny the charge, to demand proof, and to make public its own rebuttal. It has very substantial resources to make its own case and, if it can, to reveal its accusers as liars. And who is to be the judge? For two centuries the Constitution has left it up to the public to decide who's right -- not to a regulatory agency such as the FCC. Now the CIA seems to be trying to bend the First Amendment in another and less wholesome direction.