Despite calls for a cease-fire, the Philippine Army and leftist guerrillas continue sporadic clashes on this big sugar-producing island of Negros and on two other islands as well.

"It's business as usual," Bishop Antonio Fortich said here. "We've still got killing, ambushes and private armies."

About 20 deaths have been reported in small-scale clashes since the new government took power in Manila two weeks ago. The violence occurs most frequently in southern Negros, where the Communist-led New People's Army exerts its greatest influence.

Before taking power, President Corazon Aquino had called for reconciliation with the rebels, and she soon followed up with the release of more than 500 prisoners. Last Thursday, she freed the four ranking rebels, including the founder of the Communist Party of the Philippines, and established a commission to make proposals for a cease-fire.

But the guerrilla army's spokesmen and sympathizers say they want the new president to remove Defense Minister Juan Ponce Enrile and the armed forces chief, Gen. Fidel Ramos, and to meet other demands before they give up their arms. Other statements have stressed the standing guerrilla demand for pullout of U.S. bases. The military had cautioned against freeing the four Communist leaders.

The National Democratic Front, a Communist-controlled organization, has said that "while the U.S.-Marcos dictatorship has been eliminated, the structures for fascism are still there."

Negros Island, 130 miles long and with the population of 3 million, is where the New People's Army has grown most rapidly in recent years. The guerrillas have won recruits in part because of the gap between rich and poor on Negros, which is aggravated by a crisis in the sugar industry that is blamed on waste, mismanagement and low sugar prices. Some workers here make less than a $1 a day hand-cutting sugar cane.

A Catholic Relief Services study found that the majority of the island's children up to 6 years of age suffer from malnutrition.

The military has been asking church leaders, including Bishop Fortich of Bacolod, to try to persuade insurgents to come down from the hills and surrender. The Roman Catholic Church has widespread contacts with the guerrillas.

But Fortich mentioned in an interview several cases of violence on Negros in recent days indicating that the armed forces on both sides may not yet be ready for a reconciliation.

On March 2, the New People's Army ambushed a jeepload of soldiers in southern Negros killing a young Army lieutenant, the bishop said.

Five days later, he said, government soldiers killed an alleged guerrilla in the same southern area. Relatives who recovered the man's body said he had been unarmed. Also on March 7, a watch repairman who presumably was suspected of rebel links was reported to have been abducted from his village by uniformed soldiers.

Action reported elsewhere in the archipelago includes:

*In southern Luzon, Communist guerrillas ambushed a military truck on March 3, killing 12 policemen, a constabulary sergeant and three civilians, according to the official Philippine News Agency.

*On Tuesday, the same agency said, more than a 100 guerrillas overran a military post on the island of Samar. On the southernmost island of Mindanao, an Air Force helicopter gunship was reported to have killed one insurgent, one government soldier and two civilians in a strafing incident.

Here on Negros, the private armies to which Bishop Fortich referred are Civilian Home Defense Force units, whose salaries are paid by sugar planters.

In the northern province of this three-province island, Gov. Armando Gustilo, an appointee of deposed president Ferdinand Marcos, has refused to resign. According to his critics, he still controls several hundred Home Defense men. Gusilo denies that these men are under his control.

In the town of Dancalan, where the Army's 7th Infantry Battalion is headquartered, its commander, Col. George Moleta, said his men were issuing safe-conduct passes for rebels in villages known to be under their influence.

The colonel said that he had a "feeler" in one locality from about 100 sympathizers who, he said, might want "to come down from the hills" but that none had done so. He said he believed the "hard-core" Communists "will never give up."

"I consider this not a war but just trouble among brothers," said Moleta, who added that he had first and second cousins who were supporting the insurgents.

Moleta said the level of rebel activity in his area was roughly equal now to what it had been before the shift in Manila.

Moleta's records show that his troops killed a guerrilla on March 7, the same incident cited by the bishop. Two of the dead man's sisters recovered the body several days later at a location about five miles south of the town of Kabankalan.

In an interview, the sisters said that villagers told them their brother was unarmed when he was killed. The villagers also said that the man was stabbed by government soldiers before being shot. But Moleta insisted that the man was killed in an armed "encounter."