A MONTH AGO, Nicaragua seemed ready to resume a civil war that could only have ended with ravaging of the country and the victory of an authoritarian regime either of the left or the right. Today it is just possible to hope Nicaragua is on the way to becoming a democratic society. It is a fragile but stunning prospect, and Nicaraguans deserve to know that other democratic societies are watching their passage intently and cheering them on.

What happened was that American (and Guatemalan and Dominican) negotiators offered the parties a choice that they, in their distrust and pride, could not have framed for themselves. The offer was not to accept a solution drawn by the negotiators but to embark on a process by which all groups interested in participating could work out their country's common future. The process involves preparing for an early-1979 plebiscite on whether President Somoza stays in office, and planning for a transition running up to a national elections in 1981.

President Somoza, under duress, joined the process, and is now moving towards putting his own power to a popular test. He has respected opposition demands to lift martial law, declare a wide amnesty and end censorship. Substantial elements of the opposition accepted, too, and in so doing agreed to suspend their earlier insistence that the Somoza family at once quit power and depart the country.

The Sandinista guerrillas and some of their civilian allies have stayed aloof from the new process. They and others fear that the wily Somoza will not play fair. But they have not broken off contact with opposition moderates, and they have not resumed war. For the time being, no party seems ready to take upon itself the burden of balking peaceful change.

This is not the first time American diplomacy has reached out to find and embolden and strengthen the democratic moderates of a torn country. It is a chancy enterprise. Merely for trying, the United States has been accused of 1) faking a solution in order to pour the old Somoza wine into new bottles and 2) maneuvering to freeze out leftist forces interested in altering not only the government but the social structure.

But it is at the least premature to conclude that the administration is trying to cook the outcome. Let the doubters join the process and test their logic and their strength in the Nicaraguan political arena. Surely that is their best way to help end the 45-year-long Somoza nightmare and to usher their country into a new dawn.