MANAGUA, Nicaragua (AP) _ Unidentified gunmen raided and burned down a pro-Sandinista radio station's transmission tower on the eve of planned demonstrations against the government of President Violeta Chamorro.

The radio station manager, William Grisby, estimated damages at more than $200,000. He did not speculate on who carried out Sunday's attack.

Grisby, a Sandinista and deputy in the National Assembly, has had public differences in recent weeks with some Sandinista leaders.

His station, La Primerisima, is a cooperative that follows the political line of the opposition Sandinista National Liberation Front. The Sandinistas have been increasingly at odds with the government in past weeks.

The leftist Sandinistas governed Nicaragua until April, when they were succeeded by Mrs. Chamorro's U.S.-backed coalition.

Her forces beat the Sandinistas in February elections that signalled an end to a nine-year insurgency by U.S.-supported Contra rebels.

In recent days, the Sandinistas have issued calls for mass protests against the new government. They have planned nationwide marches for today to protest scheduled massive firings by the government and other austerity measures.

Describing the attack at the transmission station, Victor Sanchez Lopez, who was on duty there at the time, said four men came to the tower claiming to be inspectors for the Interior Ministry.

''They forced me out of the room and then sprayed gasoline all over the equipment and set it on fire,'' he said.