President Carlos Humberto Romero said today that his government will begin a "national forum" of meetings with political and other groups next week to try to ease nationwide unrest that has included more than 50 deaths and the rebel occupation of three foreign embassies during the past 15 days.

A special emissary sent here by the Venezuelan government met Thursday afternoon for the first time with negotiators from the Popular Revolutionary Bloc, a militant peasant student organization that has held Venezuelan Ambassador Santiago Ochoa and seven others captive in their embassy since May 11.

Meanwhile, French Foreign Ministry representative Philippe Cuvillier has been meeting daily for a week with Bloc negotiatiors with little apparent progress. French Ambassador Michel Dondenne, 62, and five others have been held inside the country's embassy since May 4 by 16 Bloc members.

The Costa Rican Embassy was also occupied May 4, but the hostages later escaped.

While the militants, who are believed to be armed with pistols and machetes, have allowed the Venezuelan hostages to talk to visitors through embassy windows, French Ambassador Dondenne was not seen for eight days until Wednesday, when Cuvillier demanded that he be brought to the second-floor embassy window to allay fears that he was dead or seriously ill.

The Bloc, which also has occupied San Salvador's downtown cathedral and at least seven churches in and around the capital has demanded the release of three of its members who it says are in government custody.

The militants have refused to talk to the government directly, and instead have insisted that the special French and Venezuelan envoys serve as go-betweens, hoping their governments will pressure the Salvadoran government.

Courses of action open to the two emissaries are limited, however, since the government has consistently denied arresting the missing Bloc members or having any knowledge of their whereabouts.

The government has suggested that the missing three either went underground or have fled the country.

Early Thursday, five security agents were killed, reportedly by guerillas claiming to be members of the Popular Liberation Forces, a clandestine Marxist group the government alleges has ties to the Bloc. Another man wounded in a May 8 shootout in front of the cathedral also died yesterday, bring the death toll from that confrontation to 25.

The cathedral shooting occurred during a demonstration supporting the embassy occupations. Witnesses said troops fired without warning at approximately 200 peaceful protesters.

While security officials and the minister of defense subsequently blamed the various shootings on members of an "international subversive conspiracy," President Romero in a broadcast speech Thursday night chose to take a softer approach toward El Salvador's problem.

Without mentioning the embassy occupations or the deaths, Romero called on "all Salvadorans of good will together to find effective solutions to our problems" through a "national forum" with participation of the government, political parties, students, the church, professional and labor organizations and other "legally recognized" groups.

The Bloc, whose membership is estimated at more than 20,000, will not be allowed to participate in the dialogue, Romero said, because it is considered an illegal organization.

In addition to the dialogue, Romero promised "absolute liberty" for all parties and citizens to participate in municipal and congressional elections scheduled here next March.

"If necessary," Romero said, "I am ready to propose the legal reforms that may be pertinent to promote the democratic process."

The promise was an apparent reference to widespread local and international charges of fraud in 1977 when Romero, an Army general, was elected.

Romero expanded on his promises in a news conference this morning, and said that details of the "national forum" will be released next week, and will include the selection of representatives to various "working commissions" to study the country's problems.

At the press conference, Romero reiterated his promise that the nation's security forces would "continue the struggle against anarchy," which he said was promoted by an international communist conspiracy.

He again denied that the three missing Bloc members were in government custody, and he noted that the government had already released two Bloc leaders arrested last month. CAPTION: Picture, President Carlos Humberto Romero offers 'forum' with "legal" organizations. UPI