The government of Philippine President Corazon Aquino overrode objections from its military today and released four imprisoned members of the Communist Party of the Philippines, including two of its top leaders.

The releases, which include that of Jose Maria Sison, a founder and first chairman of the party, are part of Aquino's policy of reconciliation with the country's Communist rebels. They appear to signal a consolidation of her authority over the military leaders who led last month's rebellion against then president Ferdinand Marcos and boosted her into power.

In another development, a lawyer in last year's trial of defendants in the assassination of Corazon Aquino's husband, Benigno Aquino Jr., said two of the military men charged and later acquitted in the 1983 slaying had confessed their guilt.

Attorney Lupino Lazaro also said new witnesses, who had been afraid to testify during the rule of Marcos, had come forward since his departure last week, offering new evidence that justified reopening the trial.

In remarks reported by the official Philippine News Agency, Lazaro said a team of lawyers was tracking down the military officers accused in the killing, most of whom are still in the country. The most prominent defendant, Marcos' armed forces chief of staff, Gen. Fabian C. Ver, fled with Marcos to Hawaii last week. Ver, 24 other military men, and one civilian were acquitted of all charges in connection with the killing.

[The Associated Press reported from Manila that Lazaro, in an interview, claimed that those implicated by the two defendants "will include . . . definitely the president and the first lady," referring to Marcos and his wife, Imelda.]

Prospects for a cease-fire by the insurgents of the New People's Army, the Communist Party's armed wing, remained uncertain, as Defense Minister Juan Ponce Enrile and Sison spoke cautiously about the chances for reconciliation.

Although Sison, who has been jailed for more than eight years, did not specifically renounce violence under questioning at several press conferences, he said he signed a document promising "not to seek to overthrow the government by violent means or force." He said he would be spending his time lecturing and writing a book about Marcos.

He also said he would be interested in traveling to the United States, if he were granted a visa, to visit his relatives, including his mother and several brothers and sisters.

The four prisoners were freed this afternoon after a wait of several days during which Enrile had expressed the military's concerns to the government.

Besides Sison, the others were Bernabe Buscayno, head of the New People's Army, and Rubin Alegre and Alex Berondo, who were accused of being members of a guerrilla liquidation squad. It was not clear whether the three signed similar pledges renouncing violence.

Sison, Buscayno and Berondo met Aquino at her office shortly after their release and thanked her for freeing them. They offered to support "positive aspects of the Aquino administration." Sison, 47, who had been jailed since November 1977, seemed in good physical condition.

Smiling and joking at an evening press conference, Sison exuberantly answered questions, stopping only when his lawyer protested that he and the other released prisoners had missed their dinner.

At the conference, held in a Catholic school in a Manila suburb, nuns listened attentively and seemed delighted at Sison's lively banter.

Sison's smile diminished only slightly as he described, in answer to questions, the torture he said he suffered at the hands of his military guards.

"The most difficult experience . . . was being shackled to a cot on a 24-hour basis for seven months, and on a 12-hour basis for another 11 months," he said. "I was in an isolation cell -- practically a box" for more than six months, he said, adding that he had "morally forgiven" his torturers.

Both the Communists and government officials suggested that further initiatives to end the fighting should come from the other side.

Another Communist Party prisoner who was ordered freed earlier but was not released until today told reporters that moves made so far by Aquino were insufficient to win the rebels' agreement to a government-proposed six-month cease-fire. "I think they will wait for further developments before they lay down their arms," said Isagani Serrano, 38.

The president has said she will seek a cease-fire with the guerrillas and name a commission to negotiate with them but has insisted that they must turn in their arms as part of an accord.

Like the other ex-prisoners, Serrano emphasized that he was not speaking on behalf of the party, saying that he had lost touch with his comrades while in prison.

In a press conference before the prisoners were released, Defense Minister Enrile warned that the rebels were continuing to fight and that reconciliation would be difficult.

"I think every possible peace effort should be explored," he said, "but I also realize that the leaders of the Communist Party of the Philippines are seekers of power, and they will use every means to accomplish their end."

Aquino's spokesman, Rene Saguisag, conceded that military men "in the field" had opposed releasing the Communist leaders. "They asked, 'What's the point of arresting a man one day if he's to be released tomorrow?' " he said.

Although Enrile has insisted that the military would follow Aquino's orders, the release of Sison and Buscayno was seen as the most concrete example so far of Aquino's willingness to assert authority over the military. Conceding that Enrile has bowed to civilian control "so far," Sison maintained that "Mrs. Aquino must assert herself over the military."

Sison called Aquino "a well-intentioned president seeking the cooperation of the broadest possible range of forces, including possibly the Communist Party of the Philippines."

Sison expressed concern about Aquino's recently appointed Cabinet ministers, who, for the most part, come from the Filipino upper class and business community.