MANAGUA, Nicaragua (AP) _ The highest-ranking anti-Sandinista rebel leader to be granted amnesty by the Nicaraguan government arrived here Tuesday from Honduras, where he had defected and taken refuge in Mexico's embassy.

Efren Mondragon Rivera, a former commander in the Nicaraguan Democratic Force (FDN), said at an airport news conference that he sought asylum two months ago at the Mexican Embassy in Tegucigalpa, Honduras.

He said he had served since 1982 with the FDN, which is based in Honduras and is the largest of the three main rebel forces.

Nicaraguan officials said Mondragon Rivera is the highest-ranking rebel leader to accept an amnesty first offered by the Sandinistas in 1983. More than 500 rebels have been granted amnesty by the leftist government.

Mondragon Rivera said the FDN has about 12,000 troops, with about half of them operating in northern Nicaragua. FDN leaders in Tegucigalpa have said the FDN force numbers 17,000.

Mondragon Rivera did not say what his duties were in the FDN, although it is known that he was once a member of the national guard under the Somoza regime which was overthrown by the Sandinistas in 1979.

When asked who was directing the FDN, Mondragon Rivera said it was CIA agents. He said there had been Argentine military advisers in the past but that they no longer are with the FDN.

''The CIA maintains its military advisers in order to prepare the (rebels) especially in sabotage and ambush of the army,'' he said.

Mondragon Rivera also said he did not think the rebels would win their war because they are short on military supplies and food and have low moral.

He also said FDN members who abandon the organization often are captured and killed by the rebels and their bodies buried in clandestine cemeteries in Honduras.