TEGUCIGALPA, HONDURAS, JUNE 15 -- Nicaragua today shot down an aircraft that it said flew into Nicaraguan territory from Honduras and fired missiles at a military base. An informed source here confirmed that the plane belonged to the anti-Sandinista insurgents known as contras but said the plane was only dropping leaflets.

According to a Sandinista radio broadcast, the unidentified aircraft flew into the province of Nueva Segovia, in northern Nicaragua, early this afternoon and attacked a military post at Cerro el Doradito, 130 miles north of the capital, Managua.

The broadcast said the Sandinista Army fired antiaircraft missiles that hit the plane, and it crashed across the border four miles inside Honduras. The plane went down in the Cerro el Tigre sector of Paraiso province in southern Honduras, the Sandinista radio said.

A source close to the Nicaraguan rebels here said the plane was a small aircraft that was "not delivering arms or engaging in fighting."

The source said the pilot was "slightly injured" when the plane came down in Honduran territory. He said the plane was probably hit by machine-gun fire but not by a missile.

The contras have not been known to possess aircraft in their limited inventory that are capable of firing air-to-ground missiles.