Nicaragua prevented opposition figure Arturo Cruz from visiting his country today, and a government statement said the onetime ambassador could not return until he renounces support for antigovernment guerrillas.

Cruz, who led a boycott of last November's elections in Nicaragua, was prevented from boarding a plane to fly from San, Jose, Costa Rica, to Manangua to deliver a proposal for peace talks between the government and the guerrillas, Cruz and airline employes said.

Until late last year, Cruz had kept his distance from the guerrillas while pursuing a nonviolent political strategy against Nicaragua's Sandinista government. Last Saturday, however, he joined guerrilla leaders in signing a document calling for peace talks to begin by March 20.

"Mr. Cruz ceased to be a member of the civilian opposition when on March 2 he formally aligned himself with the counterrevolutionary forces," the Nicaraguan Embassy in Washington said in a statement.

It said Cruz could return to Nicaragua under an amnesty law, approved by the National Assembly in January, which would require him first to give up support for armed struggle against the government.

Cruz stepped down last year from a job at the Inter-American Development Bank. He previously has traveled to Nicaragua without interference. Cruz said in a telephone interview that when he reached the airport today, he was barred from boarding.

"An airline representative told me that they had received instructions by cable from Nicaraguan migration authorities that no airline can give me passage to go to Managua," Cruz said.

A spokesman for Nicaragua's Interior Ministry said the CIA had a plan "already in place" to have Cruz killed in Nicaragua and blame the government.

Cruz broke with the Sandinistas in 1982 after serving as a member of the ruling junta.