MANILA, OCT. 29 -- The slaying of two U.S. airmen and a Filipino-born U.S. Air Force retiree outside Clark Air Base yesterday has dramatically altered the complexion of the ongoing political violence here and shattered the long-held dictum that foreigners -- particularly Americans -- were generally immune from the Philippines' civil war.

"Before, we were never the targets, so it was kind of like being in New York City or the Wild West, with shooting going on all around you but you were never affected," said one U.S. Air Force officer who asked not to be named. "But when they start killing Americans, that's a whole new ball game."

President Corazon Aquino, beginning a day-long trip to Cebu in the central Philippines, told reporters she was "very sorry" about the killings.

{U.S. Under Secretary of State Michael H. Armacost, after a four-day visit to Manila, said, "We deplore all killings, but we confront this violence around the world," Reuter reported. He said the killings "won't change U.S. relations with the Philippines."}

Whether the perpetrators of yesterday's attacks are communist assassins or renegade right-wing soldiers, analysts and foreign diplomats said the two groups appear to share a common aim: to destabilize Aquino's centrist government and create a situation where the two extremes ultimately will compete for political power.

"Does it matter if it was the left or the right? The effect is still the same, really," one Asian diplomat said today. "The point is, there is a constant escalation of targets here. It's gradually heading toward an all-out confrontation."

Meanwhile, suspected communist hit squads killed five people in two separate attacks today. Gunmen killed two soldiers and two civilians in an early morning attack on a food market. Later, a policeman riding in a jeep was gunned down by three men.

The two American servicemen and the Air Force retiree were slain in separate, apparently coordinated attacks while walking or riding in their cars within two miles of Clark, a facility in Pampanga Province north of here. Clark houses the 13th U.S. Air Wing. A U.S. Air Force officer came under attack in his car but escaped injury.

The dead servicemen were identified as Airman 1st Class Steven M. Faust and Sgt. Randy Davis, and the retiree as Herculana C. Manganta. A Filipino also reportedly was killed while trying to aid Faust.

U.S. and Philippine military officials declined to speculate on the identity of the assassins. But Gen. Fidel Ramos, the Armed Forces chief of staff, warned that the communist New People's Army had resorted to "an ongoing resurgence of violence through . . . liquidations and assassinations."

Today's attacks and the slayings of the servicemen at Clark bring to 14 the total number of civilians and U.S. and Philippine military personnel assassinated by unknown gunmen in the past 48 hours.

Ramos said he ordered additional Philippine troops deployed in the area around Clark, in Angeles City, and Subic Bay Naval Station in neighboring Olongapo Province, the repair yard for the U.S. 7th Fleet. Ramos said the increased security was "to prevent further attacks on United States personnel."

Maj. Gen. Donald Snyder, the 13th Air Wing commander, went on U.S. armed forces televison tonight and warned, "I don't consider that Americans are out of danger because there are still threats of incidents." Snyder said reports in local media that a communist hit squad had threatened to kill more Americans were still "unconfirmed." But he added that U.S. officials were taking the threats "very seriously."

Snyder did not specify which reports he was referring to, but earlier this morning an anonymous caller told the Manila bureau of Agence France-Presse that communist urban partisans were behind the attacks and intended to kill 10 Americans in retaliation for the delivery of 10 armored personnel carriers to the Philippines last Friday as part of U.S. military aid.

Snyder said authorities were conducting an "intensive investigation" to find the killers.

A Philippine police spokesman in Angeles City said four suspected communist hit men were apprehended during an early morning raid on a village near Clark. Two .38-caliber revolvers, several rounds of ammunition and documents reportedly detailing assassination plots were seized. But the police spokesman later said the four were not likely involved in yesterday's slayings.

Base spokeswoman Maryellen Jadick said some temporary duty requests in the Philippines had been canceled and that Snyder was "highly discouraging those people {stationed elsewhere} who want to come here."

U.S. military personnel based at Clark were restricted to "essential travel only" outside the base. At Subic Bay, servicemen were advised not to wear their military uniforms off the base.

U.S. military officials also increased patrols at off-base housing areas where about two-thirds of the military personnel reside, according to Pentagon spokesman Fred S. Hoffman.

He said American and Filipino military forces had increased joint patrols around the perimeter of Clark.

Violence always has been a feature of political life here. But in the past, the violence was governed by unspoken rules of the game.

Cabinet members were never targets; soldiers did not fire on fellow soldiers; the communists never attacked economic targets.

Over the past 18 months, however, all of those rules appear to have been broken.