PEOPLE IN THIS COUNTRY swing from boredom to alarm at the prospect of coups or revolutions in Central America. The ho-hum reaction is a traditional North American response to turgid developments south of the border. The alarm follows when the inadequacies of ho-hum start to be recognized. Until last fall, the United States remained indifferent to El Salvador, the hemisphere's most active volcano. Then, the administration got scared. It decided that the risks of a "second Nicaragua," a second Central American revolution that might go Cuba's way, outweighed the comforts of its preferred non-intervention policy. It started intervening, in a political sense, to an extent that has made El Salvador the most interesting laboratory of American policy anywhere in the world.

The scene could hardly have been less inviting. For more than four decades the United States had contributed to the building of a vast social explosion, which was already coming, promising a terrible civil war and a geopolitical calamity. Then the administration began trying to muffle or channel that explosion. Military intervention, Vietnam style or any style, plainly was out, although it had its partisans in the Pentagon and among the unreconstructed Salvadoran right. The classic liberal response, to bring along social reform and popular participation by easy stages, was no less irrelevant in the context of El Salvador's advanced deterioration.

The policy finally chosen, or partly chosen, was to make an audacious gamble on the Salvadoran military: to transform key elements of it from custodians of a rotting, violent status quo to caretakers of reform. This has involved a delicate appeal to the patriotism and institutional interest of the armed forces by providing supplies (and the prospect of training) and by seeking their commitment to truly vast efforts at social redress, centering on land reform. The risk of this policy lies in the corruption of substantial parts of the military and their identification with repression. The promise of the policy lies in its rediness to deal with a real center of power, one with important elements interested in modernization, and to harness those elements to change.

Many of the broadly based political groups that will have to be brought into the new order to make it work are frankly skeptical, if not contemptuous, of the idea that the military includes potential allies, not just assured foes. A deep pessimism inclines many citizens to feel that progress can come only by cataclysmic violence. This puts an extraordinary burden on the military to earn popular confidence by limiting violence and making land reform work. It puts a special burden on the United States to continue its wager on the armed forces only if they show themselves worthy of it.