Opponents of President Ferdinand Marcos, deriding his implied threat of a return to martial law, said tonight they will mount new antigovernment protests that will include demonstrations against President Reagan if he comes here in November.

"If Mr. Reagan comes, we will prepare a proper welcome for him," said an opposition leader, Jose Diokno, emphasizing that he meant "protest actions."

His comments came as Manila was still counting the dead and injured from a violent confrontation between police and youths after a peaceful rally that called on Marcos to resign.

At least 10 persons--two firefighters, two marines and six civilians--died in the riot, according to The Associated Press, and Marcos said 11 were dead. The government said 66 civilians and 59 military and police personnel were injured.

The violence provoked a new round of recriminations from all sides today, with Marcos linking the riot directly to his political opponents and rally organizers and implictly threatening to revive martial law.

"I warn the opposition, do not force my hand," Marcos declared in a television appearance this morning. "Do not compel me to move into extremes that you already know of. If necessary, I will do so."

Marcos imposed martial law in 1972 and lifted it in 1981, but he retains some of its powers. "You misread our capability if you think that one night's rioting is going to deter us," Marcos said.

Some of the toughest verbal blows were struck today by the leader of this country's 39 million Roman Catholics, Cardinal Jaime Sin, who in part blamed the Marcos government for blocking the path to national reconciliation.

The government's "lack of openness, the atmosphere of evasiveness that it fosters, its adherence to practices that bring back memories of Mr. Goebbels of Nazi Germany--these are not calculated to inspire faith and confidence," the cardinal said. "Unless they are changed, reconciliation cannot be achieved."

It was also disclosed today that the White House has sounded out the cardinal for a possible meeting if Reagan visits in November.

A church newspaper reported that the proposal was made from the White House in early September, about two weeks after the murder here of opposition leader Benigno S. Aquino Jr. His death has led to the largest antigovernment demonstrations in the country's history.

Such a visit would give Reagan a chance to appear publicly with an important figure who is often, but not always, at odds with Marcos. Sin is frequently critical of Marcos, but at times cooperates with him and lends the government his prestige and influence.

Reagan's trip here is criticized by the opposition as lending support to Marcos in his struggle to survive the effects of Aquino's assassination on Aug. 21. The belief is widespread that the Marcos government was in some way responsible.

A visit with the cardinal might soften the criticism somewhat but it probably would not deter the political opposition from staging protests.

In Washington, State Department spokesman John Hughes said the United States "deplores all violence as a means of resolving political problems" and hoped that "both the government and the opposition will deal with their political problems in a way that contributes to political stability, the strengthening of democratic institutions, and respect for human rights."

Except for protesting Reagan's arrival, however, the opposition indicated today it has not planned its next assaults on the government. Leaders said Marcos' threat of martial law would not deter them but were hesitant to discuss specific actions. Agapito Aquino, brother of the slain man, said a sit-down strike was one possibility.

It was clear that the anti-American flavor of yesterday's mass rally will be continued in future protests organized by a broad-based organization known as JAJA, an acronym for "Justice For Aquino, Justice For All."

"It firms up the movement," said Diokno, a veteran opposition figure.