President Ferdinand Marcos today accused Cardinal Jaime Sin, the highest ranking prelate of the Roman Catholic Church in the Philippines, of fanning "the flames of rebellion" and encouraging violence by calling on Filipinos to join street demonstrations against the government.

In his sharpest public attack on Sin, the archbishop of Manila and a persistent critic of Marcos' 19-year-old rule, the president also accused the cardinal of violating the constitution and "trying to destabilize our government."

In a nationwide television address, Marcos warned that he would no longer tolerate unauthorized demonstrations. He threatened to arrest their leaders and participants, including businessmen and professionals, who heed Sin's call to join students in a "parliament of the streets."

A number of prominent business community leaders, professionals and politicians have announced their intention to join a rally and march Sunday to protest the violent dispersal by security forces of a demonstration on Sept. 27.

Sin immediately dismissed Marcos' warning. He said he would go ahead with plans to say mass before the demonstration and denied Marcos' assertion that he was violating the constitution's provision on separation of church and state.

The potential showdown between Marcos and Sin comes at a crucial stage in the political opposition's campaign against the government and could decisively affect the future role and influence of the opposition moderates, according to Philippine observers.

Sin and the centrist opposition apparently want to prevent radical opponents of Marcos from taking over the movement against him and fomenting a violent confrontation with his security forces. Marcos seems determined to head off any broadening of the street protests against him at a time of financial crisis and political tension, the sources said.

Philippine negotiators are locked in talks in Washington with the International Monetary Fund and representatives of 483 creditor banks. At issue are Manila's economic recovery program and its requests for new loans.

In Manila, meanwhile, some tension has been reported at the presidential palace and within the military over a potentially explosive official report expected shortly on the assassination last year of opposition leader Benigno Aquino.

In his television address, Marcos warned that continued demonstrations could undermine creditors' confidence in Philippine stability and wreck the recovery program.

He said bankers and analysts of the Philippines may be led to wonder whether the country "is so unstable that it cannot control its own citizens" any longer. He added that "it will not be possible to be so tolerant anymore, because if we were to continue to allow this illegal rule of the mob in the streets, then our creditors would certainly deny us any support and would come to the conclusion that the government is unstable, weak, incompetent and unable to enforce the law."

Marcos warned that if the demonstration planned for Sunday goes ahead without a permit, "we may be compelled to make arrests, of leaders as well as followers."

Opposition sources said businessmen were applying for a permit for the demonstration at the Welcome Rotunda in the metropolitan Manila municipality of Quezon City, scene of a confrontation Sept. 27 in which one person was fatally shot by riot police and a dozen others wounded.

Security forces also used tear gas, water cannons and clubs to disperse about 3,000 persons who had gathered at the rotunda to protest the breaking up of a rally near the Malacanang presidential palace Sept. 22. Some protesters responded with rocks and small homemade bombs that injured several riot policemen.

The morning after the dispersal, at least five bodies of unidentified youths were found, and opposition spokesman expressed suspicions that they were protesters caught and killed by the police or military.

In what he said was an effort to stop "a Saturnalia of sadism and violence" by security forces, Sin urged Filipino businessmen and professionals on Tuesday to "join the parliament of the streets" and demonstrate peacefully "for an end to the violence and the authoritarianism of the dictatorship."

Marcos, however, asserted today that "the parliament of the streets has always been violent . . . so when you encourage participation in the parliament of the streets, you encourage violence."

Marcos said Sin's words "tend to fan the flames of rebellion." He added, "It means he would encourage killing, perhaps rebellion, in the sense that it would be bloody and violent."

Marcos called on Sin to "help us return to sobriety" in this predominantly Catholic nation. "Let us not wreck our country," he said.

In reply, Sin insisted he was going to say mass before the rally and asked, "Shall I be arrested for saying mass?"

"I am not violating the principle of the separation of church and state," he said, insisting that he had a pastoral duty to judge the "morality of certain government actions." Sin added that "using violence on peaceful demonstrators and killing them is immoral, and I have a duty to try to stop it."

Sin had appealed to Marcos last night to order his forces "back to the barracks" during Sunday's demonstration.

He condemned what he called a "sinister pattern" of increasing use of force against demonstrators, which he said showed the "undoubted determination of the Marcos regime to stifle freedom of dissent and freedom to assemble peacefully for redress of grievances."