MANAGUA, Nicaragua (AP) _ A brush fire started by farmers to clear their land set off explosions Monday at a nearby air base ammunition dump, wrecking a Soviet-made cargo carrier and damaging a second airplane, police chief Rene Vivas said.

Vivas said a gust of wind spread the fire to the air force base adjoining Managua international airport, and the blasts destroyed the AN-26 cargo plane. He said a second air force plane, also parked on a runway, was damaged but gave no further details.

Officials said the airport was immediately shut to traffic until further notice as a precaution.

The midday explosions were heard throughout the capital, but Vivas told reporters that although many residents were alarmed, ''There are no victims and there was no major damage.''

Vivas said farmers were burning brush and weeds to clear their field for planting when a strong wind spread the flames to open ground at the air base where explosive material and fuel was stored.

Fire brigades at the airport quickly brought the blaze under control, Vivas said, who added he doubted ''very much'' that the explosions could have been caused by sabotage.

U.S.-supported Contra rebels have been fighting Nicaragua's leftist Sandinista government for nine years, and President-elect Violeta Barrios de Chamorro's civilian administration takes office for a six-year term April 25.

Most of the rebels have refused to surrender their weapons and demobilize until Mrs. Chamorro takes office and exercises control over the Sandinista- dominated military.