Taking advantage of the changing political climate here, the Philippines' highest judicial body, the Supreme Court, has begun to reassert its independence from President Ferdinand Marcos.

Two recent decisions supporting civil liberties have stunned lawyers here.

In one, the Supreme Court, reversing its earlier decision not to question the right of Marcos to order detention without trial for one year, ordered the release of two suspected subversives.

In the other decision, the court ordered the military to return the printing press and office equipment of the antigovernment tabloid We Forum, which was shut down in 1982 for questioning Marcos' reputation as the Philippines' most decorated war hero with 28 medals.

Human rights lawyers expressed cautious optimism about a possible relaxation of Marcos' control.

"It was an interesting departure from previous trends," commented human rights lawyer and politician Jose Diokno, whose Flag group of lawyers defends political detainees. Francisco Chavez, head of another human rights group, called Bonifacio, said, "I am not overenthusiastic, but it is a healthy sign that the Supreme Court is applying the law."

One of We Forum's lawyers, Rene Saguisag of the Mabini lawyers group, said he was surprised by the ruling but warned, "I don't know yet if two swallows mean that summer is ahead and we can put the winter behind us." The Flag, Bonifacio and Mabini groups led militant lawyers in a two-day boycott of the courts and picketing of the Supreme Court in December to protest the judiciary's alleged subservience to Marcos.

Raul Roco, president of the Integrated Bar of the Philippines, which regulates the country's 32,000 lawyers, said of the two Supreme Court decisions: "They are manifestations that the extraordinary powers given to the president by acquiescence have reached a point where they cannot be tolerated."

The majority of the 14 high court judges are Marcos loyalists and supported the president when he declared martial law in 1972.

The lawyers agreed that the August 1983 assassination of Marcos foe Benigno Aquino had triggered the political change. The press is freer, and a revitalized Parliament, with one-third of the seats held by the opposition, is keeping the government on its toes.

Although Marcos has retained full power under the constitution, he has had more difficulty exercising it since Aquino was slain. "Marcos has lost some control over the judiciary," observed Diokno, the human rights lawyer.

Some lawyers said they had begun to note changes in Supreme Court rulings a year ago when it made some unexpected but minor decisions against the government. In one such ruling, the court rebuked the government's elections commission when it took over the recounting of the votes in a disputed parliamentary race. In another, it granted opponents of nuclear power a right to a public hearing on the safety of a $2 billion nuclear plant.

But these rulings were loose change, said We Forum's Saguisag, as they did not come close to hacking at the core of Marcos' power.

The Supreme Court has failed to rule, however, on suits filed by the Integrated Bar of the Philippines questioning the legality of decrees issued by Marcos that give the government authority to deprive anyone declared a subversive of property and citizenship.

A Supreme Court source said that Chief Justice Enrique Fernando, who is to retire in July at the age of 70, may not want to act on such "politically hot potatoes."