MANILA, OCT. 29 (THURSDAY) -- Two American servicemen and a Filipino-born U.S. Air Force retiree were shot and killed yesterday in separate but apparently coordinated attacks outside Clark Air Base, marking the first known terrorist incidents against American targets here in more than a decade.

In a fourth incident, an American Air Force officer in his car came under fire about the same time as the other attacks, but he escaped injury, according to Maj. Thomas Boyd, a spokesman at Clark, the American-leased facility in Pampanga Province north of here.

All of the attacks occurred within two miles of Clark, in different areas of Angeles City and within 15 minutes of one another, beginning shortly before 4 p.m. yesterday.

A man claiming to represent a communist hit squad telephoned the Agence France-Presse news agency in Manila this morning, saying the killings were in response to the delivery by the United States of 10 V150 armored personnel carriers to the Philippine Armed Forces on Friday.

The caller said seven more Americans would be killed, one for each of the armored vehicles. The call could not be verified as authentic. The communists have never been known to telephone news organizations to claim responsibility for killings.

Most analysts said the slayings could have been the work of either communist assassins or rebel right-wing military officers who want to destabilize the government of President Corazon Aquino.

If the communists were linked to the slayings, it would mark a potentially dramatic escalation of their insurgency that has taken its campaign of violence from the countryside to city streets.

One serviceman, identified by Clark spokesman Boyd as Airman 1st Class Randy A. Davis, was killed while walking near a McDonald's restaurant in Dau, and another was killed on the road to Carmenville, a mostly American subdivision. He was identified as Sgt. Steven Faust. {The Pentagon said he was an airman first class from Pasadena, Texas}.

In that incident, military officials said, a Filipino who came to the scene to help the American also was killed.

A car driven by an American, identified as Capt. Raymond Pulsifer, came under fire at about the same time on the road to the Sunset Valley housing subdivision, but the assailants missed.

In the fourth attack, retired Tech. Sgt. Herculana Manganta was killed at Hensonville, a military housing area, as he drove his car across a bridge, according to Boyd. A spokesman at Clark said this morning that the Air Force was uncertain whether Manganta, who was born in the Philippines, had obtained U.S. citizenship.

Maj. Gen. Donald Snyder, the 13th Air Force commander, went on the armed forces television station here and asked military personnel to "maintain very, very good prudence" and restrict off-base travel to major roads. "We're not sure who's perpetrated these crimes," he said.

The slayings come after weeks of repeated warnings from the communist New People's Army that they were prepared to escalate their 19-year-old insurgency by attacking American targets.

The most recent issue of Ang Bayan, the Communist Party's official newsletter, carried an unsigned statement in which the party threatened to attack American military facilities and business interests.

Earlier this month, the Northern Luzon chapter of the New People's Army held a clandestine news conference, and a rebel spokesman, Ruth Firmeza, announced, "If there is another coup or martial law, we will hit the U.S. imperialists, all American personnel, military, diplomatic or what." He added that "U.S. facilities are also targets" and announced a "hit list," naming prominent Filipino politicians and some journalists, including Newsweek magazine correspondent Melinda Liu.

The slayings outside Clark bore a striking resemblance to recent slayings in Manila by "sparrow units," the New People's Army's urban assassination squads, named after the bird because of their smallness and their members' quick moves.

The serviceman killed near McDonald's was walking toward the restaurant when three men appeared and opened fire at point-blank range, police said.

A Philippine police spokesman said the three gunmen fled aboard a "jeepney," a makeshift bus popular here. The spokesman in Dau said two empty shells from a 45-caliber pistol were found at the scene.

"Sparrow" assassinations in Manila have generally followed the same pattern, with a group of three men or women approaching their victim on a street, opening fire at close range with handguns and then fleeing aboard jeepneys where they easily blend into the crowds.

If the communists were found to be responsible for yesterday's killings, the United States could be faced with new policy risks. So far, Washington has for the most part avoided being directly drawn into the Philippines' counterinsurgency effort.

Although the communists earlier had issued threats to attack Americans, analysts were cautious about assessing responsibility for yesterday's killings. Despite the obvious propaganda value of the threats, the communist guerrillas in the past have been reluctant to attack Americans, fearing that a wider escalation of their insurgency might risk drawing in American forces on the side of the government.

The last known attacks by communists on Americans came in the mid-1970s at Subic Bay Naval Station.

Some observers noted that right-wing military rebels have been active in an area near the Air Force base, and they suggested that the attacks on the Americans may have been perpetrated by right-wing soldiers trying to blame the communists and to destabilize the Aquino government.

Renegade Lt. Col. Reynaldo Cabauatan, who is wanted in connection with a January mutiny, has been sighted recently in the Clark area and held a news conference in a house on the grounds of the base, according to several reporters who attended the press conference. Last week, U.S. Ambassador Nicholas Platt said he had "no evidence" that the event took place.

The killings occurred at a time of rising Philippine nationalism -- recently emphasized by the new foreign secretary, Raul Manglapus -- that often has translated into anti-American sentiment here. Moreover, sensitivities have been sharpened as the agreement for the retention of Clark Air Base and Subic Bay Naval Station comes up for renegotiation next year.

This week, the growing anti-American mood was highlighted by a diplomatic dispute involving a U.S. Embassy military attache, Lt. Col. Victor Raphael, who was accused in the press of "meddling" in the Aug. 28 attempted coup by being inside a rebel-held military camp and at one point trying to dissuade progovernment troops from attacking the rebel position, according to the press reports.

Platt confirmed that Raphael was inside the camp during the coup, but maintained at a press conference last Thursday that Raphael was only "doing his job" and remained a "trusted member" of the embassy staff. But as the incident showed signs of escalating this week, with both houses of Congress announcing plans to investigate, the embassy yesterday announced that Raphael would be sent back to the United States this week.

The embassy, in a statement, said the transfer "is no reflection on Lt. Col. Raphael's performance" and that the charges against him were "unfair and unwarranted."

The case has underlined a new tension in U.S.-Philippine relations, as Manila has tried to recast its traditional special relationship with the United States.

Manglapus told a press conference yesterday that the Philippines should begin to broaden its relations to end its heavy dependence on the United States. "I think it's time to renew this attitude and to recognize that we do have also special relationships with Asia, then Europe and then the United States," the foreign secretary said.

Some analysts have predicted that Manglapus' new nationalistic tone in foreign policy will make it more difficult for the United States and the Philippines to reach an agreement on retaining the military bases past 1990.