THE CARTER ADMINISTRATION, speaking for a country that was itself implicated indirectly in an assassination plot in Chile not that long ago, acted boldly in demanding the extradition of three Chilean police officers implicated directly in the Letelier-Moffitt murders. At the same time, by submitting its request to the Chilean Supreme Court rather than making it as a political demand to the Pinochet government, the administration put itself under a certain obligation to accept the court's ruling, as predictable as it might be. That court has now issued its final denial of extradition. The ruling slides over the impressive evidence of Chilean complicity gathered in an American courtroom. It leaves the administration in a bind.

Now, there can be no real doubt that the three officers, and their superiors, did plan to blow up exiled opposition leader Orlando Letelier; an American associate, Ronni Moffitt, died with him at Sheridan Circle three years ago. And the junta's current strategy is plain. It must have figured it had paid its dues by sending back home the American expatriate who, along with three Cuban exiles, was convicted earlier this year for the two murders. With the incident fading into time, the junta presumably thought it would not have to pay heavily for turning down the extradition request. Who really expected President Pinochet to produce suspects who might lay off the blame on him?

Still, the junta unquestionably did direct the murder of an exile on American soil. Only the little people who did the dirty work have been called to account. The junta did not respond in good faith to the offer to have its courts deal with the case on the merits. The officers are free. A precedent has been set to fight international terrorism half-heartedly.

Some political steps can be taken for show -- recalling the ambassador. Then it gets hard. Little aid remains to be cut off. Cutting off access to critical private loans appeals to some congressmen, but not to many, and not to even the rights-minded Jimmy Carter: "inconceivable . . . under any circumstances. This would violate the principles of our own free enterprise system."

There remains not much more than a possible stiffening of attitudes by the government, aroused citizens groups and like-minded private lenders. The expectable result would not be so much to get the police officers as to convey that decent people cannot countenance terror. It would be good if such a message could be conveyed unequivocally. But that was precluded when the United States welcomed, if it did not help to power, the very junta that was to murder Orlando Letelier.