Salvadoran President Jose Napoleon Duarte, in a dramatic reversal of policy, offered a general amnesty today for all political crimes and proposed that the leaders of leftist guerrilla groups meet with him -- unarmed -- next Monday to discuss "their incorporation into the process of democracy."

In a speech to the General Assembly, he suggested that the meeting take place at 10 a.m. on Oct. 15 in La Palma, a village in El Salvador's Chalatenango province between rebel-held and government-controlled territory.

Duarte made clear in a news conference afterward that his invitation was limited to the commanders of the guerrilla armies and did not include the leaders of the Democratic Revolutionary Front, the civilian political arm of the guerrillas.

These leaders -- disaffected Christian Democrats and members of left-of-center parties -- live in self-imposed exile because, they say, they fear they would be killed if they returned to El Salvador. In November 1980, five leaders of the front who had returned to El Salvador were kidnaped and murdered.

Duarte told the assembly that the leaders of the Democratic Revolutionary Front do not understand the "new reality" in El Salvador because they live outside the country.

Duarte said that the political leaders "have no authority over the military commanders" and that the discussion "should be with valid interlocutors -- those who have the authority to reach decisions."

To assure guerrilla commanders that they would not be ambushed if they attend the La Palma meeting "without weapons of any kind," he said, the government is inviting the archbishop of San Salvador and the papal nuncio to witness the meeting, along with "the world press."

In addition, Duarte said, "I have complete support of the Army high command" for the safety of the meeting. The ultimate guarantee, he said, is that "I, too, am putting my life on the line. I am going to attend alone, without any protection. Think what it means for the president to go to a place where he, too, can be ambushed."

Representatives of the guerrillas called on Duarte to prove his intent by sending them a proposal, through an intermediary, detailing security measures and a possible agenda, Julia Preston of the Boston Globe reported from Mexico City. If Duarte does, "undoubtedly our reponse will be positive," said Mario Lopez, a member of the diplomatic commission of the rebel front.

The U.S. Embassy in San Salvador applauded Duarte's speech as a "major step," while political and diplomatic sources in the Salvadoran capital said in telephone interviews with Washington Post correspondent Robert J. McCartney that the president's initiative took them by surprise.

"President Duarte's offer to meet with the guerrilla military leaders is a major forward step in the process of national reconciliation based on democratic elections and a clear advance in the search for peace in Central America. We applaud this speech and these actions and fully support them," the U.S. Embassy said in a statement read over the telephone to McCartney who was in Mexico City.

In Washington, State Department spokesman Joe Reap said Duarte's offer "is a clear advance in the search for peace in Central America."

La Palma is on a main highway on the edge of the guerrilla zone. It is a village of artisans known for their pottery and is one of the few places in the country where a visitor can drive from government to guerrilla territory and back without encountering difficulties.

The date set for the meeting is the fifth anniversary of the overthrow of a right-wing junta by a group of reform-minded junior officers.

It is also the deadline set by the Contadora group -- Mexico, Panama, Colombia and Venezuela -- for responses from the five Central American nations to the text the group has proposed as the basis for a regional peace. The four-nation group, which first met on Panama's Contadora Island, has been trying to negotiate a Central American peace agreement for 2 1/2 years.

In his speech, Duarte announced that El Salvador would seek changes in the text "for the verification and control of everything that has been agreed to." He explained to reporters later that the text does not provide El Salvador with assurances against destabilization.

"We fear," he said, "that we will be left helpless against support for the guerrillas from other countries, including Nicaragua," unless broader guarantees are provided. Duarte proposed that the next step be direct negotiations among the five Central American countries -- Nicaragua, Costa Rica, Guatemala, Honduras and El Salvador -- "to try to correct all these difficulties of the Contadora act."

The initial reaction to Duarte's offer from Nicaraguan sources was that his announcement was intended to distract attention from El Salvador's reservations about the Contadora plan, and to drive a wedge between Salvadoran guerrilla leaders and their civilian allies. Nicaragua supports the Contadora proposal.

Nevertheless, the Nicaraguans recognized the impact of his gesture before the international audience here.

For Duarte, it was a reversal of the stand he had held since taking office June 1, when he said no dialogue with rebel representatives could be undertaken until a "climate of security" has been established in the country. This was interpreted to mean the securing of his own authority against threats from far right politicians and death squads allied with them. Duarte's aides recently had suggested that no talks could be envisaged before next year.

Before his election, Duarte had spoken of dialogue to end the civil war but had warned that talks were not possible with the civilian opposition leaders until they established control over the guerrilla armies. He had never before suggested direct talks with the rebel military commanders of the five armies in the Farabundo Marti National Liberation Front. While the rebels have charged that Duarte cannot get rid of the groups within the armed forces that cooperate with the death squads, the president has said that the leftist politicians cannot control the guerrillas.

There had been two meetings outside El Salvador in 1983 between a government peace commission and representatives of the guerrillas, but they ended in acrimony and helped to provoke a wave of right-wing death squad killings. This weekend, however, a major prisoner exchange was completed after preliminary contacts this summer between the Army and guerrilla representatives.

The left -- both civilian and military -- repeatedly has proposed a dialogue and has criticized Duarte for reneging on his earlier promise of one. But the rebels have rejected government insistence that the agenda be limited to the terms under which they could participate in legislative elections next March.

Today's statement by Duarte left the content of the talks open. He announced that "in due course I shall propose to our legislative assembly a general amnesty for political crimes." There have been four other amnesties in El Salvador since the 1979 coup. In the most recent, last year, several hundred political prisoners were released, but few guerrillas turned in their arms. It was not known if the amnesty proposed today would be different from the previous ones.

Duarte said his government is now "exercising control over abuse of authority and eliminating all methods of repression," so the need for rebellion no longer exists.

"This means," Duarte went on, "I am offering the safety and security of a political place within a pluralistic, democratic system." And he asked the guerrilla leaders to discuss the details and scope of this offer.

Asked to elaborate, Duarte kept the agenda broad and vague, saying, "What I am offering is an opening of the political, democratic space, so those sectors who wish can join in the search for the social peace we all want."

As evidence of his good intentions, Duarte said the government would free later today a union official, Hector Recinos Aguirre, and nine other men held without trial since 1980 on weapons charges.

McCartney reported the following from Mexico City:

Duarte's initiative was unexpected in part because his aides had said previously that a dialogue with the left would have to wait until the start of next year, at the earliest.

"This was a surprise for sure," said one middle-level diplomat who asked to remain anonymous. "I do not know of anybody who was expecting anything like this before the March election."

Some Salvadoran political sources suggested that Duarte had acted now because he believed he had the military initiative. So far this autumn the guerrillas have not launched a major offensive as they did beginning in early September last year.

In one indication that Salvadoran conservative political parties might accept Duarte's move, Salvadoran Supreme Court President Francisco Jose Guerrero called the initiative "an effective effort in the search for peace."

Guerrero, who was asked for his comments in a telephone interview, was the candidate of the conservative National Conciliation Party in last spring's election. His party is less extreme, however, than the Nationalist Republican Alliance of former major Roberto D'Aubuisson, which has strongly supported a military victory over the guerrillas.