THE PAUSE in the fighting in Nicaragua's civil war has created an opportunity for sorting things out politically. The opportunity consists of the stated readiness of President Anastasio Somoza and his opposition to accept mediation, and of the inter-American community to provide mediation. So sharply are the lines now drawn in Nicaragua as a result of guerrilla-led popular attacks on the government and the brutal repressions of Somoza's National Guard that the prognosis for a political solution must be guarded. Yet the chance is there.

In Washington, the Organization of American States came within one vote of passing a resolution that everyone understood chiefly as a harsh condemnation of President Somoza's violence. Swallowing much of its distate for any approach smacking of intervention in a member state's internal affairs, the QAS went on to ask Nicargua to accept its "friendly cooperation" in mediating the dictator's dispute with his domestic foes. Under this formal umbrella, the United States has now won Managua's agreement to elt Washington conduct "a search for peaceful solutions with the participation of interested political opposition groups." Translation: With the United States quietly leading the way, the QAS is trying to manage the process of Nicaraguan political change.

It's premature to think that President Somoza, by accepting mediation, is preparing for his early resignation. That is what his domestic rivals and many international critics devoutly desire. An astute technicaian, he may have accepted the mediation proposal in order to influence the choice of mediator (presumably he'd prefer like-minded military governments) and to confound his Nicaraguan opponents. All the same, a mediation process could conceivably develop some momentum of its own. It will require concessions by all sides, not to speak of skill on the part of the mediators, whoever they turn out to be. It is the only available substitute for the open politics that the Somoza dynasty has denied for 45 years.

The Nicaraguan opposition, including the guerrillas, seems ready to work to install democracy promptly. There is some risk, however, that President Somoza will be misled by his relatively few remaining American supporters - 70 congressmen have just hailed him as a "long and consistent ally" - into thinking that he does not have to bend. His American friends do no service by encouraging him on a course that could lead not to an orderly transition but to renewed civil war.