MANILA, NOV. 9 -- Communist guerrillas have issued a new threat to attack American soldiers conducting armed patrols in the area around Clark Air Base, calling the patrols "an affront to Philippine sovereignty."

In a clandestine press conference yesterday with Filipino reporters in a village near Angeles City, home of the American air base, an unidentified rebel spokesman for the communists' Central Luzon command reportedly said the armed patrols were an explicit example of direct American participation in the counterinsurgency campaign here. The patrols were instituted after the slaying of three Americans outside Clark on Oct. 28.

The rebel spokesman echoed an earlier warning from Saturnino Ocampo, a leading figure in the communist-led National Democratic Front, who said in a signed statement Friday that Americans would now be "targets for attack" for what he called U.S. government "meddling" in the Philippines counterinsurgency campaign.

The specific warning that Americans here are no longer immune from attack marks a decisive shift in the rebels' longstanding policy. Previously, Ocampo and others have said Americans would not be targeted because there was no evidence of U.S. involvement in the war against the guerrillas.

Analysts had previously believed the communists were shifting that policy because of anger over the American government's stepped-up delivery of weapons and hardware to the poorly equipped Philippine armed forces. Others suggested the communists could be trying to disrupt negotiations scheduled to begin next year over the retention of Clark and the other large U.S. facility, Subic Bay Naval station in Olongapo city.

The patrols at Clark, conducted jointly with Philippine police and military personnel, have also been criticized by some congressional leaders. Opposition Sen. Juan Ponce Enrile, the former defense minister, was quoted in an interview yesterday as saying, "Allowing off-base patrols by armed U.S. servicemen shows that the Aquino government can no longer protect American lives.

"But more than this, it is a violation of the bases agreement, and an incursion into Philippine sovereignty, an insult to the military and the government," Enrile said.

Late last week, a progovernment senator, former justice minister Neptali Gonzales, warned that patrols outside Clark by armed American soldiers raised the risk of clashes between U.S. troops and the communist guerrillas who are active in the area. "History tells us that just one encounter between the dissident {communists} and U.S armed units will lead to escalation, and this might lead to further polarization of the people," Gonzales told a Senate public hearing.

Despite the criticism, and the most recent communist warning, Clark officials said the patrols will continue.

Maj. Thomas Boyd, Clark's director of public information, said American troops have been patrolling the peripheral areas of Clark and the off-base housing units where Americans live since 1979. "The change has been that they are now carrying weapons, as they should do considering the threats."

Boyd said accusations that the patrols violated Philippine sovereignty were "illogical" since all patrols are conducted with units of the Philippine police or military.

"Anytime anyone carries a weapon off base, it is done with the express permission of Philippine authorities," he said.