Under orders from President Corazon Aquino, the Philippine armed forces began releasing political prisoners today, in what was seen as an early indicator of whether she will be able to exercise her authority over the military leaders who helped her overthrow former president Ferdinand Marcos.

Aquino also met U.S. presidential envoy Philip Habib, who arrived this morning "to assess the situation . . . and to express support for the Aquino administration," a U.S. Embassy spokesman said.

Government television said Habib told Aquino the Filipinos had "astonished the world with their courage" in ousting Marcos without violence.

Diplomatic analysts and Filipino observers agreed that Aquino's military leaders, who are concerned about the prospective release of Communist militants who support an insurgency, were pressing her to back away from her campaign pledge to release all political prisoners as soon as possible.

This morning, Aquino ordered Defense Minister Juan Ponce Enrile to release 39 prisoners, including labor activists and lawyers, some of whom had been imprisoned for more than six years. But Aquino's military chief of staff announced pointedly that the group included no one who had taken up arms against the government.

The military today arrested Marcos loyalists who resisted the new Aquino government, including Gen. Madrino Munoz, a regional commander on the southern island of Mindanao, and Rodolfo Farinas, a mayor from Marcos' home region in Northern Luzon. Police suggested Farinas and nine aides might have been preparing to kill Aquino and Enrile with M16 rifles and other weapons discovered in their cars yesterday.

The Philippines is fighting a long-running battle with Communist guerrillas of the New People's Army in the countryside. Rene Saguisag, a civil rights lawyer on Aquino's special commission examining the cases of political prisoners, said the group would continue reviewing lists of detainees supplied by the Army and a human rights organization, and might announce "hundreds more releases by Saturday." But Saguisag also told journalists that an undetermined number of political prisoners, possibly between 10 and 100, would not be freed, suggesting that Aquino may be preparing to compromise with her military leaders on the issue.

Saguisag acknowledged that the known differences between Aquino and the military leadership over the release of political prisoners had raised some doubts.

"There are those who still think the military will try to assert authority over the civilians on this issue," he said, "but they have repeatedly said they will follow the orders of the civilian government."

Saguisag said the prisoners released today were "the easy cases," and expressed the government's sympathy with them.

But there was no indication whether the government would consider releasing leading Communist personalities such as Bernabe Buscayno, a commander of the New People's Army, or Horacio Morales, leader of the Communist Party's banned National Democratic Front organization.

The Task Force Detainees of the Philippines, a human rights organization that the Marcos government has accused of pro-Communist leanings, said tonight it counted 617 political detainees in military custody, well above the armed forces' estimate of 450. But the group also said information on human rights abuses had begun flowing more freely since Aquino's takeover.

"We've raised our count twice today as we've gotten new details from our regional offices," said Vinya Abasamis, research coordinator for the group.

Connie Sorio, a worker with Kapatid, an association of relatives of political prisoners, said, "We know that Cory [Aquino] wants to stop this, but we're really very doubtful of the sincerity" of Defense Minister Enrile and military chief of staff Gen. Fidel Ramos.

"Ramos has been only talking about strengthening counterinsurgency, and this makes us nervous," Sorio said.

Enrile, whom Aquino returned to the post he held under Marcos, and Ramos, who had been acting vice chief of staff, long have been criticized for failing to prevent or investigate abuses by the military during the Marcos years.

Ramos was criticized last September when he justified as "self defense" the machine-gunning of an unarmed crowd by militia forces, in which at least 21 persons were killed. Enrile ordered a special inquiry into the massacre, but no prosecutions have resulted.

Human rights workers fear that military officers, especially among the lower ranks and in remote areas, may actively obstruct Aquino's attempts to end the Army's role in human rights abuses. Various international human rights organizations have condemned the former Marcos government, for its alleged use of military force to detain people without trial, to torture, prisoners and assassinate political opponents.

Aquino spokesman Saguisag said the government would ignore political arrest warrants that had been issued against expatriates, thus preventing them from returning to the country.

Saguisag also said in a press conference that the government would eventually abolish the mechanism called preventive detention actions, which permitted Marcos to imprison anyone indefinitely. In the meantime, he said, Aquino would not use them.

United Press International reported the following:

Cardinal Jaime Sin, the Roman Catholic archbishop of Manila, welcomed top leaders of the new government to a mass of thanksgiving for the "people power" revolution in which he played a key role.