MANAGUA, Nicaragua (AP) _ The army said Monday that troops killed 115 Contra rebels and wounded 12 in battles in northern Nicaragua from March 11-17. Assistant Cmdr. Julio Caesar Aviles, army chief of staff in the northern region, told the newspaper Barricada several rebel leaders were killed in 45 battles.

No names were given nor was any mention made of army casualties. Barricada is the voice of the ruling leftist Sandinista National Liberation Front.

Aviles said rebel forces infiltrated Nicaragua on March 11 from Honduras and were ''well-equipped after several months of training.'' The U.S.-backed rebels, known as Contras, have fought for four years to oust Nicaragua's leftist government. Most operate from bases in Honduras.

Aviles estimated damage at about $10 million from an attack on a power station in Yalaguina in Esteli province. The attack, reported earlier, caused extensive power outages in the north.

Military sources, who spoke on condition of anonymity, said the same force was believed responsible for attacking a tobacco cooperative in Jalapa in Nueva Segovia province. Six large tobacco storehouses were set ablaze.

Aviles said the drive was part of a ''propagandistic'' effort by the rebels following President Reagan's request for $100 million in aid to the Contras.

Accounts of fighting between Contras and soldiers often vary widely. Independent confirmation is rarely possible because of restricted access to combat areas.