MANAGUA, NICARAGUA, DEC. 23 -- The Defense Ministry said today that Sandinista troops would lay down their arms after midnight to honor a two-day Christmas truce in their war against contra rebels.

Government soldiers patrolled the northeastern gold-mining region after two days of heavy battles in what the rebels called their largest offensive in the six-year war. No major combat was reported today.

Both the leftist government and the U.S.-supported rebels claimed they had achieved their objectives. President Daniel Ortega said last night that the contras suffered more than 100 dead in the attacks on three villages that began Sunday. He said 24 soldiers were killed and 23 were injured. Sixteen civilians were killed and 75 wounded, he said.

"They tried to give the impression they are a large force, to try to take the villages, thus to influence the Congress," Ortega said in a broadcast speech. Yesterday, the U.S. Congress approved $8.1 million in aid to the rebels as a stopgap measure.

The rebels said 3,000 troops backed by 4,000 support forces raided the towns of Siuna, Rosita and Bonanza, about 170 miles northeast of the capital.

The contras reported 170 Sandinistas killed, but did not report their own troop losses. They claimed to have destroyed key radar installations and captured 600 rifles and 60 machine guns.

The Sandinistas and the rebels agreed to a two-day Christmas truce proposed by Roman Catholic leader Cardinal Miguel Obando y Bravo. But talks to work out a lasting cease-fire broke down yesterday in the Dominican Republic.

In El Salvador, meanwhile, the guerrilla coalition Farabundo Marti National Liberation Front announced that conditions did not exist for a Christmas truce, as proposed by the government.