The American Institute for Free Labor Development has posted a reward of $50,000 for information leading to the arrest and final conviction of the murderers of Michael Hammer, Mark Pearlman and Rodolfo Vera, who were killed in a restaurant in El Salvador on the night of Jan. 3, 1981.

Two weeks after this announcement, Secretary of State Alexander Haig proclaimed to the world, not just his countrymen, that the fight against terrorism would replace the campaign for human rights as a top priority of American foreign policy.

What difference does this change in priority make? How will that difference be interpreted in those parts of the non-Soviet world where American influence counts? If Hammer, Pearlman and Viera were killed by irregulars allied with the state campaign to eradicate terrorism, are they still to be counted among the direct victims of terrorism? Or are their deaths now to be seen as somehow permissible mistakes or excesses of war?

In some quarters, the American campaign for human rights has been considered a device of the left; it seemed to focus more on the victims of state repression than on the victims of left-wing guerrillas. But the danger today is that the announcement of a change in priority from a pro-human rights policy to an anti-terrorist one is apt to be considered, by some key people who carry guns in Latin America, as more than a redress of an imbalance; they will construe it as a license to pursue an unrestricted anti-terrorist campaign.

In other words, it is widely believed, rightly or wrongly, that in its concern to help governments eliminate the left-wing threat in the region, the United States will now approve the fact that some right-wing countries have condoned, and condone, the methodical abduction and secret murder of thousands of suspects.

Is the State Department, and through it the Reagan administration, giving a singal of acceptance of what the Interamerican Commission on Human Rights condemned in its report on Argentina?

It it is not, someone should say so; an unclear signal can encourage new waves of state-condoned violence, more abductions and secret murders of suspects. Many people assume that Americans, even under their new leadership, do not want that, any more than they welcomed the murders of Hammer, Pearlman and Viera.

But if the State Department is signaling a tacit appearance of the methods of conterterror that some right-wing authoritarians have used in the past to eliminate and intimidate terrorists and opponents of the left and of the center, then the unclarity of the signal has its purpose: a politically astute administration would not choose to spell out its intent in this field.

Though the moral point of view insofar as it concerns the lesser-developed part of the non-Soviet world appears to be shelved by the new Republican administration, it can be pointed out that the previous administration's adherence to it amassed considerable good will for the United States in a part of the world where anti-Americanism has been an endemic disease since before the Cold War.

True, this asset in a crisis does not have the immediate eclat of a few well-placed regiments with friendly commanders well disposed to American interests. But in the most unexpected times it can make a difference, and perhaps in the long run it will make the difference.

Is it really prudent for the United States -- and for Latin America -- to disregard this moral capital, even if it was obtained by methods of negotiation, compromise and zealous respect for principle that now appear to be in disfavor and especially when it would be so cheap to conserve it? After all, it is only a matter of signals, perceptions and restraint, not money.