The Roman Catholic Church in the Philippines, long a bastion of conservative thought, has begun to speak out against the martial law government of President Ferdinand Marcos.

Led by the archbishop of Manila, Cardinal Jaime Sin, church leaders have become increasingly vocal against the martial-law system that was proclaimed seven years ago.

In a recent interview, Cardinal Sin warned of the danger of civil war if the corruption and military abuses under martial law are not curbed.

"I am trying my best to avoid the vision that I foresee from becoming a reality," he added gravely.

In a recently released pastoral letter, Roman Catholic bishops strongly attacked this corruption, as well as human rights violations in the Philippines.

The pastoral letter said the temptation to violence in the face of what it described as "manifest, longstanding tyranny" and the apparent impossibility of getting reform is not surprising.

Bishops and other church leaders close to the cardinal say Pope John Paul II's coming visit to the Philippines, the only predominantly Christian country in Asia, adds impetus to the church's new militancy. Sin has never before asked for the dismantling of martial law.

The government is reacting with unusual speed to the church's criticisms. Recently, bishops in rebel-wracked Mindanao in the south and communist-infiltrated Samar in central Philippines raised a loud outcry against human rights violations and the apparent breakdown in military discipline.

A committee was set up immediately to investigate the reports of the deaths and torture of many innocent civilians. Marcos advised his soldiers to turn the other cheek when provoked by the church.

Bishop Julio Labayen, who heads the church's Social Action group and is one of the 15 militants in the governing body of 98 bishops, said, "The complaint [about military abuses] are nothing new. What is new is that the government is giving a lot of publicity to the complaints. Everybody is getting into the act because of the pope."

The specter of the Philippines' human rights record being exposed to international publicity during the pope's visit apparently is troubling the Marcos government. Officials are aware that this particular pope does not mince words on human rights.

Nevertheless, the most attention is being placed on the role of Sin. The church's new outspokenness and, in particular, Sin's increasing militancy, may mean a change in the church's relationship with the state. There are, in fact, indications that the cardinal is guiding the protests.

He is the only person in the country who could rebuke the president. With the National Assembly powerless, the church remains the only formidable organized force apart from the military.

Thus any government must cultivate its goodwill. The government also realizes that the cardinal, a moderate, has the support of the majority of the bishops who are conservative.

Sin appears to have set in motion a series of events to shake martial law a little. As early as March, in speeches and interviews, he said he was disenchanted with martial law because of the abuses and called for an end to it.

Many observers believe the culminating effect of all this was a glittering Manila Hotel dinner last month in honor of former Senate president Gil Puyat. The opposition managed to turn the affair into a forum against martial law.

At that dinner, Imelda Marcos sat impassively while speaker after speaker unleashed a barrage of criticism against her husband's government.

In spite of his criticism, Sin hastens to add that the church can exist in any form of government, as long as it is allowed to teach the gospel and human rights and the common welfare of the people are protected.

In the interview Sin emphasized his fears that the mounting discontent may lead to civil war.

He wants a return to a normal democratic process of government because he is afraid there will be chaos when Marcos passes from the scene.

Unlike the church in Latin America where the rift with government is much wider and sometimes violent, the Philippines Catholic Church adheres closely to the Vatican line of avoiding a head-on confrontation with the Marcos government.

Sin's dissenting priests and nuns -- a small but vocal faction of the church that comprises the so-called Christian left -- prefer the Latin American brand of "the theology of liberation." Their South American counterparts have rallied the people against rightist dictatorships' violations of human rights.

To these activists Sin appears frustratingly weak and even vague. When government officials accused some church elements of working with the communists, a nun active in anti-government causes said, "Yes, the church has been infiltrated by the communists, thanks to the cardinal."

Sin explains his role by saying "The progressives in the church are the ones giving life. The conservatives are the brakes. If they are all brakes the church will not run. If they are all accelerators, the church will crash. So I, the driver, will decide when to use the brakes and the accelerator."

Former senator Jovito Salonga, a strong opponent of martial law, says of Sin, "He could have been more militant. The government will not touch him."

Church sources say Sin must play ball with the government, however, for two reasons: to prevent divorce from being legalized and to protect the church's powerful Radio Veritas, which broadcasts as far as China.

Sin sees himself as a unifier. He says he and Marcos remain friends, that it is his duty to bring complaints to Marcos, and that is the most he could do.

In judgment of himself Sin says, "When I die and God asks me what I have done, I will say I complained but he [Marcos] did not listen."