Recent assassinations of military officers, defectors from the communist New People's Army and suspected informers have interrupted a relative lull in the guerrilla war following the Feb. 25 ouster of president Ferdinand Marcos.

The death toll in this city, known as the Philippine "murder capital," is still far below last year's, when about 800 persons were killed. But military and Roman Catholic leaders are expressing concern that the communists are starting to take a tougher line as they debate a cease-fire offer and try to prevent defections from their ranks.

Meanwhile, there is wide agreement that public attitudes toward the Philippine armed forces here have improved significantly since the military-led popular revolt swept Marcos from power.

In one incident of the renewed communist activity, Wilfredo (Baby) Aquino was leaving the neighborhood of a brothel he owned in the tough Agdao slum district of this southern port city last month when his jeep came across a roadblock manned by several men wearing fatigues and armed with M16 rifles.

Without warning, the men opened fire, instantly killing Aquino, 38, a community political leader and head of a unit of the paramilitary Civilian Home Defense Force in Agdao. Also killed in the fusillade were his driver and a 28-year-old woman identified as Aquino's mistress. Police recovered 58 M16 bullet casings.

Responsibility for the killing of Aquino, who was not related to the Philippines' new president, Corazon Aquino, was promptly asserted by the New People's Army, the armed wing of the Communist Party of the Philippines. It said in a rare published statement that the "regional partisan command of Davao city" had meted out the death penalty to Aquino for a long list of "crimes" that allegedly included gunning down striking workers. "Let his death serve as a sobering reminder to all fascist forces, military and paramilitary alike, that the New People's Army will never allow crimes against the masses without retribution," the statement said.

While Wilfredo Aquino's death went largely unlamented because of his unsavory reputation, there have been signs lately that other killings are costing the NPA its Robin Hood image here as the military consolidates its public position.

"People are less afraid, less antagonistic toward the military," said one Filipino priest. He said the attitudes toward the military had changed -- and dissatisfaction with NPA excesses had increased -- even in Agdao, which has been dubbed "Nicaragdao" because of heavy communist influence there in recent years.

According to church sources, among the more ruthless killings by the communists recently have been the killings of at least 30 insurgents suspected of being military "deep penetration agents" -- also known among the rebels as "zombies" -- in the area of the northern Mindanao city of Butuan. The suspects were "brutally tortured" before they were killed, said one knowledgeable priest. He said the bloody purge, which started in October 1985 and has continued this year, was widely seen as "a real black eye for the rebel movement."

Diplomatic sources confirmed that such a purge took place after the military had succeeded in placing a woman infiltrator on a Communist Party commission that oversees operations on Mindanao. They said the woman was caught and executed, setting off the purge.

Since the February revolt against Marcos, the NPA also has trained its sights on members who heeded President Aquino's call to abandon the communists' 17-year guerrilla war. According to the Rev. Emeterio Barcelon, who is involved in a privately run rehabilitation program for those who quit the rebels, at least three former insurgents who sought to join the program have been assassinated by their comrades.

Col. Marcelo Blando, the commander of a Scout Ranger regiment in the province of Davao del Norte, said one NPA defector was released from a military camp at 2 p.m. on May 12 because he had gotten a job. By 5 p.m. he was dead, Blando said.

The commander of an NPA company in Davao Oriental Province, Alexander Navarro, received a warning that the NPA was unhappy with him a day after he surrendered and met President Aquino May 23, church sources said.

Despite high hopes that many rebels would quickly abandon their struggle following the departure of Marcos, the result so far is only a trickle. In southeastern Mindanao, according to the military, about 200 NPA rebels have surrendered out of a total of about 8,600 thought to operate on the island.

Liquidations of military men and suspected civilian informers also have continued, although apparently on a lesser scale than before. On May 5, Col. Alfredo Felisco, 58, the chief of the Army Reserve Command in Davao, was shot 13 times by three unidentified men as he was walking home from a friend's house. He reportedly was the highest ranking military officer killed in Davao and the second officer of the Army Reserve Command to be gunned down in a month by suspected NPA hit teams.

On May 21, vendors Vilma Boca, 20, and Lolita Quinola, 21, were shot in the head as they were taking a shortcut home, police said. The killers were not identified, but observers here noted that street vendors often are used as informers by the military.

At the same time, killings of NPA suspects by the military also reportedly have continued. Davao newspapers reported five such killings, known here as "salvagings," in the first four days of May. Generally, however, the level of salvagings, like that of NPA liquidations, has fallen sharply, residents say.