HAVING SURVIVED an internal guerrilla challenge last fall, President Anastasio Somoza of Nicaragua seems now to have survived an international political challenge as well. The American-led "mediation" team, appointed by the Organization of American States to bring about "friendly cooperation" among warring Nicaraguans, has come to a halt. Mr. Somoza has kept the loyalty of the National Guard through a time of testing, divided and discombobulated his political opposition and, by appeals to fellow military rulers, prevented the closing of a hemispheric ring. He has probably gained political advantage by defying his erstwhile American patrons and demonstrating his political skills.

In retrospect, it seems plain that Mr. Somoza accepted mediation in order to manipulate it to stay in power, while the opposition, understanding Mr. Somoza too well, accepted it only begrudgingly, never committing enough to the process to make it work for them. Forty-five years of Somoza family rule had produced a society unpracticed in the ways of political compromise. The arrogant Somoza commanded the military power and knew that many of his civilian opponents were more afraid of their associates on the left than of him. The opposition, united mostly against his personal rule, was vulnerable to being split along class and ideological lines.

The mediators, realizing President Somoza was exploiting their presence to advertise his good will, could not fail to take into account that they were in his country only by his sufferance. All the same, they succeeded in putting together a proposal, for a plebiscite, acceptable to moderate opposition elements. The guarantees the opposition demanded, however, reflected their justifiable suspicion of the Somozas. Aware that the dynasty had long rigged voter registration, for instance, the opposition demanded that there be no registration. Fearing that the president would capture any process he joined, the opposition insisted he leave before the plebiscite. Such demands made it easy for Mr. Somoza to say no.

We think he has made a major mistake. The consequences of his cleverness will be further protests, violent and othrwise, and further violence and repression by the state. A wise leader, rather than exploiting his countrymen's weaknesses, would have accepted the mediators' help in conciliation. The United States, called in to mediate, went much further by pressing President Somoza to resign. It now has few usable diplomatic cards left. The next stage of Nicaragua's agony will apparently be conducted by Nicaraguans themselves.