BY DECEMBER, Guatemala's president, Efrain Rios Montt, said last July, he intended to defeat the guerrillas in Quiche province. Many listeners scoffed: Marxist-led guerrillas had been in the field for 20 years, and Gen. Rios Montt was widely regarded as little more than a religious eccentric. Post reporter Christopher Dickey recently toured Quiche and other former guerrilla strongholds, however, and found as others have that nine months after the coup that brought the general to power, the guerrillas have been crushed and normal life is returning.

Gen. Rios Montt did it by sending the army on repeated sweeps into the countryside, demanding that the Indians who live there choose sides. Those who cooperated were offered "beans and rifles." Those who denied the army their full support paid harshly: since last spring, hundreds if not thousands of peasants may have been killed, either by the army or the guerrillas, and tens of thousands made refugees. In the process, the army dried up much of the sea in which the guerrilla fish swam.

Guatemala's civil war is hardly over. The class, ethnic and religious disparities that have fed it have not disappeared, the guerrillas still have their sanctuaries and friends, and some of the government's own policies are bound to kindle resistance. It seems undeniable, however, that Gen. Rios Montt has achieved the kind of quick security gains that few had thought possible. But the means he has employed strongly suggest that Gen. Rios Montt has created not so much an opportunity as an obligation to start sharing power and healing the country.

Indirectly, the United States has a continuing responsibility in Guatemala arising from its sponsorship of the coup that toppled the constitutional government in 1954. But directly, it has no responsibility for what Gen. Rios Montt has done, thanks to an aid cutoff that came in response to the wretched human rights records of earlier regimes.

The aid cutoff did not lead Guatemala to improve its human rights performance: not that much aid was flowing, and other suppliers were quickly found. Paradoxically--as in a grim and awful joke-- what the cutoff did was to free Mr. Rios Montt to conduct a very bloody security policy, free of American hectoring. Guatemala conducted this policy-- and from its distance the Reagan administration approved it--in the conviction that establishing its authority was the first duty of a government. Be that as it may, the duty of that government now is to show, if it can, that it has values that are worth supporting. In the circumstances, with the worst presumably behind, it may make sense for the United States to resume a modest aid tie with a view to influencing the next stage.