TERRORISTS KIDNAPPED Napoleon Duarte's daughter last Tuesday, a cruel stroke intended, the Salvadoran president suggested, to make him lose his "serenity." It could turn out to be the latest desperate act of the guerrillas, who, increasingly reluctant to take on the army in the countryside, have moved in to terrorize the cities. The murder last June of a group of Salvadoran civilians, killed in the attack that took the lives of four American Marines, brought the new tactic to foreign attention. That attack also provoked the guerrillas' civilian front to criticize such acts for their "negative political effects" abroad and in El Salvador.

The human rights issue in Central America is being partially turned around. Formerly, almost all the known atrocities were committed by or at least attributed to the right. The left fanned the issue and tried to make controlling the right the test of a regime's worthiness. Government and elements of the right have not since become angels. But they have been under American pressure to close down the death squads. Results have been substantial in El Salvador, inadequate so far among the Nicaraguan contras.

Meanwhile, however, terrorism of the left has become more evident, notably in El Salvador: not just devastation of economic targets but murders and kidnappings. It is not simply that the administration tries to shift people's focus. These are real events tending to undercut the left's earlier moral pose. Some human rights groups are starting to take this development into account. Some members of the Latin left, for reasons that include a keen concern for their credibility, are, too.

The United States cannot stop for a minute pressing its friends to improve on this score. This administration remains under a burden to show it is not soft on anticommunists in respect to human rights. Its latest idea sharpens the point. The administration wants to sponsor, in Costa Rica, an academy to teach the police forces of Central America modern and humane methods. The last American experience in training foreign police left Washington tainted as a teacher of torture. To dull the risk now, as some suggest, let Costa Ricans do the teaching.

The administration also has it in mind to resume military aid to Guatemala, if its November elections come off well. The Guatemalan military's rights violations lost it U.S. aid in the 1970s. Thus did Americans avoid further taint. Freed of the American connection, however, the Guatemalan military went truly crazy. The way to see whether a new connection with a civilian Guatemalan government is feasible is: very carefully.