The Reagan administration's activist policy of promoting change in the Philippines is raising expectations here of greater U.S. involvement in fighting a spreading Communist-led insurgency once today's presidential elections are out of the way.

Containing that insurgency has become the chief goal of U.S. policy in the Philippines and has led the Reagan administration to abandon its commitment to "quiet diplomacy" when dealing with the flaws of a friendly government that subscribes to its global anticommunist credo.

The administration has sought to distance itself from President Ferdinand Marcos while continuing to push him, openly and insistently, to enact sweeping reforms and to step up action against the guerrillas if he is reelected.

It is understood that senior U.S. officials also have concluded that Marcos is deliberately covering up for the military men they believe killed opposition leader Benigno Aquino in August 1983. While these suspicions are not being voiced in public, they have influenced the administration's view of Marcos.

But those concerns appear to be secondary to rising fears in Washington that Marcos, enfeebled by a disease that has severely affected his kidneys and discredited at home by his perceived role in the Aquino assassination, simply is unable to contain the guerrilla movement known as the New People's Army, which U.S. officials portray as "rushing in to fill the vacuum" the government has left in the countryside.

This has led U.S. officials to accept with equanimity the prospect of Marcos losing to opposition candidate Corazon Aquino, Benigno Aquino's widow, despite her lack of experience and her disinclination to support the continued presence of two important U.S. bases in the Philippines.

"If she wins, things may get worse but they may also get better," said one U.S. official in Washington. "If Marcos stays, we know they cannot get any better."

While disagreeing on virtually all other issues, Aquino, senior aides to Marcos and clandestine spokesmen for the political front of the New People's Army share the view that the activist U.S. policy of recent months appears to foreshadow increased U.S. involvement here.

"Filipinos are divided by the American rediscovery of the Philippines," said Labor Minister Blas Ople, a Marcos associate. "Some think of it as intervention in our affairs, while others think that it is time the United States reciprocated some of our maudlin interest in the U.S." He said that he hoped this rediscovered interest would lead to increased U.S. understanding of and aid for the Philippines.

Ople has revived terminology associated with American debates over the Vietnam War to label State Department officials who seek change here as "interventionist hawks" who are more worried about the Communist insurgency than is the Marcos government.

"Doves, who retain sound political instincts" and will not push Marcos as hard, include President Reagan and Vice President Bush, Ople predicted. Ople suggested that the U.S. leadership would extend its support for Marcos after the election.

Echoes of Vietnam also are found in remarks made by spokesmen for the National Democratic Front, an illegal political organization reportedly run by the Communist Party of the Philippines and the New People's Army guerrilla movement.

"We expect an escalation after the election, with more direct U.S. involvement, whether Marcos or Mrs. Aquino wins," said a source close to the front's leadership. "If Mrs. Aquino wins, it may hasten American intervention" because she will be able to get Congress to agree to greater U.S. support, he suggested.

"We have avoided attacking the Americans at the bases here, because we want the United States to stay out of this conflict. We know that if you attack the Americans, you draw them in. But we know the Americans are studying intervention here now."

In a separate discussion, two members of the front's secretariat said that U.S. involvement in the war would cause the guerrillas to reconsider their stated policy of not seeking arms from the Soviets.

"Our arms come 95 percent from capture, and we buy the other 5 percent," a front official said. "If there is greater U.S. involvement in trying to eliminate us, we will look again at our policies. It would depend on how we size up the conditions" the Soviets attach to supplying arms.

The nature of the guerrilla movement has become an issue in the election campaign here, with Marcos accusing Mrs. Aquino of being "dangerously naive" about the guerrillas, whom he describes as "ruthlessness itself."

His campaign has sponsored wide circulation in movie theaters of "The Killing Fields," a film about the atrocities committed by the Khmer Rouge after they came to power in Cambodia in 1975. Marcos has cited the film repeatedly in his speeches as portraying the future of the Philippines if Aquino is elected.

Aquino has described the New People's Army as being a small core of dedicated Communists surrounded by people outraged or victimized by abuses committed by Marcos' forces. She predicts that many of the guerrillas will lay down their arms if she is elected.

The debate over the nature of the New People's Army, which has about 15,000 armed troops and operates freely in an estimated 20 percent of the Philippines' 40,000 villages, is also certain to be a key factor in the Reagan administration's decisions about fulfilling the expectation here of a significantly enhanced U.S. role.

Spokesmen for the National Democratic Front portray their coalition and the New People's Army as following the direction of the Communist Party of the Philippines.

But they deny that the guerrillas engage in gratuitous violence or resemble the Khmer Rouge in any other way. To do so, they contend, would cost them the support of the Philippine countryside. "If you try to terrorize the people, they will kill you the moment you turn your back," one front official said.

The New People's Army "wants socialism, but it is committed to passing through a national democratic revolution first that could last for years. Entrepreneurial capitalism would be permitted to exist."

Asked how political moderates could be certain that they would not simply be eliminated if the guerrilla army wins the war, a member of the front's secretariat responded bluntly: "This is a challenge for the moderates to address. We encourage people to take up arms. If they put their hopes in elections like these, then they will get nowhere. The problem with the moderates is that they are more interested in getting rid of us than in getting rid of Marcos."

The United States is providing $54 million in military aid to the Philippines this year as part of an annual $180 million payment for the use of Subic Naval Base and Clark Air Base, the largest U.S. military installations abroad.

The Reagan administration already has signaled that it will request $100 million in military aid for the Philippines for fiscal 1987 if today's elections are not marked by visible wholesale fraud, and if Marcos undertakes reforms within the military.

The chief U.S. demand is a change in the highly politicized promotion system in the Philippine Army, which is staffed at the top by aging officers whose chief job is protecting Marcos.

"The guys who are supposed to do the fighting in the field know they will never get promoted that way if things stay as they are," said one U.S. official who has visited the Philippines frequently. "This army is starved for resources," he added. "It is no wonder the troops are out moonlighting or stealing from villagers rather than fighting the guerrillas. We must help restore a tradition of professionalism that Marcos has almost destroyed."

During the campaign, U.S. officials are known to have stressed that a military coup to prevent Aquino from winning probably would destroy any support for new military aid from the United States. U.S. officials also have been pressing Marcos to remove Gen. Fabian Ver, his chief of staff and head of the unit that took Benigno Aquino into custody shortly before he was shot to death.