MANAGUA, NICARAGUA, NOV. 22 -- Two members of the Nicaraguan Air Force stole a small Soviet-made military plane yesterday from an airfield in southern Nicaragua and flew it to Costa Rica, the Defense Ministry confirmed today.

Costa Rican officials said the single-engine plane made an emergency landing in stormy weather on a private airstrip near the northern town of Liberia, a Costa Rican newspaper, La Nacion, reported.

Officials said the airmen were in Costa Rican custody and had requested asylum.

On Oct. 25, Maj. Roger Miranda Bengoechea, a top aide to Sandinista Defense Minister Gen. Humberto Ortega, defected to the United States. The defections come as the leftist government here is aggressively pursuing its war against U.S.-backed rebels, known as contras, and loosening its political control under the terms of a regional peace process.

Second Lt. Carlos Gadea Arostegui and airman Jose Jacinto Ramirez Mendoza, whose rank has not been disclosed, "kidnaped" the AN2 passenger plane from an airfield near the south-central town of Juigalpa, a Defense Ministry communique said.

Nicaragua has asked Costa Rica to return the aircraft and is investigating the two defectors for "failure of flight discipline," according to the communique.

The plane, forced down by blustery rain, landed shortly after 5 p.m. at a farm about 40 miles south of the border, Costa Rican officials said.

Costa Rican security police accompanied the soldiers this morning to San Jose, the capital, police officials said. The Costa Rican government has issued no statement.

The Juigalpa region was the scene of bloody battles between Sandinistas and contras in recent weeks.

Nicaragua's Air Force has been hard-hit this year as increasingly skilled contra fighters, trained and armed by the Central Intelligence Agency with Redeye heat-seeking missiles, downed at least 12 military helicopters.