MANILA, OCT. 30 -- President Corazon Aquino today said she did not believe Wednesday's slayings of two American servicemen and a U.S. Air Force retiree represented a new threat to U.S. military and business interests in the Philippines.

A leading communist urban terror group disavowed the slayings.

In a news conference with foreign correspondents, Aquino also tried to allay growing fears among the Philippines' Southeast Asian neighbors that political instability and violence may make it too dangerous for Manila to host a regional summit scheduled for mid-December.

Several officials and diplomats from countries in the Association of Southeast Asian Nations (ASEAN) have voiced reservations about traveling to Manila for the forum -- the first in a decade -- which many fear may attract terrorists.

The shootings of the Americans, the first such attacks here against foreign targets, were expected to reinforce fears that Aquino may not be fully in control of the country.

"The summit meeting will go through as mentioned in December," Aquino said. She said Philippine security officials already are meeting with their counterparts in the other five Southeast Asian capitals and are "taking all measures to ensure that each head of state and head of government be given maximum protection."

Aquino said she had not received a full report on the slayings outside Clark Air Base in Angeles City and said reports that the Alex Boncayao Brigade, a communist urban terror group, was behind the killings were still "unvalidated." Asked if the situation had deteriorated to the point where American interests in the country were in danger, Aquino replied curtly, "I don't think so."

The U.S. Embassy here is advising Americans to take "appropriate security precautions" because of the risk of more attacks against U.S. citizens.

"There are reports which cannot be confirmed indicating there possibly could be attacks against Americans in Manila and elsewhere in the Philippines. No time frame has been indicated," an embassy spokeswoman said.

Clark remained under intense security today, and U.S. officials continued to restrict travel off the base to essential trips.

Most analysts believe that the killings were perpetrated either by communist assassination squads, known as "sparrow units," or renegade right-wing military officers. Both groups aspire to destabilize the Aquino government and perhaps provoke Aquino into taking a dramatic step, such as declaring martial law or a state of emergency.

The killings appeared to bear the mark of "sparrow" assassinations, which have become almost commonplace in Manila since March. Many analysts suspect, however, that right-wing military rebels may have launched the attacks, knowing that the communists would be blamed.

The "sparrows" are suspected of having killed about 86 people in Manila this year, including 36 military officials, 33 police officers and 15 civilians, according to Philippine military officials.

"Sparrows" were immediately suspected in the slayings outside Clark, and early yesterday an anonymous telephone caller to the Manila bureau of Agence France-Presse claimed responsibility for the attacks on behalf of the Alex Boncayao Brigade, the terrorist wing of the communist New People's Army. Most analysts discounted the claim since the group has never before telephoned to claim credit for attacks.

Today, the Alex Boncayao Brigade issued a statement in Manila denying it made the telephone call and saying it had nothing to do with the killings. The statement said the brigade operated exclusively in Manila, while the attacks took place in Pampanga Province, north of here.

Despite the denial, many analysts still suspect the communists -- primarily because of their own past threats to escalate their 19-year-old insurgency by striking American targets.

The most recent, English-language issue of Ang Bayan (Our Country), the newsletter of the central committee of the Communist Party of the Philippines, carried an unusual threat against Americans in an article justifying the use of sabotage.