The State Department official in charge of Latin American affairs arrived here early this morning for a brief, hastily planned visit amid warnings by Nicaraguan leaders of a "deteriorating relationship" between the revolutionary Sandinista government and Washington.

U.S. Embassy officials here maintain that the visit of Thomas O. Enders, assistant secretary of state for inter-American affairs, was simply to "get acquainted." Speculation was widespread, however, that a diplomatic rupture may be imminent.

Asked if Enders were here to help repair relations, U.S. Ambassador Lawrence Pezzullo said, "I don't see any deterioration."

But the Sandinistas are clearly concerned.

Nicaraguan Foreign Minister Miguel D'Escoto said shortly before he met with Enders for an hour that he believed Enders came "to see what might be done to better this increasingly deteriorating relationship."

The most recent troubles in the difficult relations between revolutionary Nicaragua and Washington started July 31 when the U.S. Senate ratified a treaty with Colombia giving up any U.S. claim on three tiny islands more than 200 miles east of Nicaragua's Atlantic coast. Both Colombia and Nicaragua claim the islands.

This Saccio-Vazquez treaty was signed by Colombia and the United States in 1972, but had languished unratified partly because of Nicaraguan objections to it.

The Reagan administration maintains that the treaty in no way prejudices Nicaragua's interests.

After meeting D'Escoto, Enders talked with Nicaragua's ruling junta. The U.S. Embassy said Enders had no immediate comment.