According to the office of Sen. Paul Tsongas (D-Mass.), an article Wednesday concerning the mediating role of the "Tsongas group" in El Salvador contained inaccurate identifications. Neither Rep. James M. Shannon (D-Mass.) nor former U.S. ambassador to El Salvador Robert E. White is a participant in the group.

U.S. Senator Paul Tsongas (D-Mass.) and several liberal activists in the United States have worked together since early this year as private intermediaries in contacts between the Salvadoran Army and its guerrilla opponents, U.S. and Salvadoran sources said today.

The group's efforts, sources said, helped create a climate that allowed President Jose Napoleon Duarte to offer the peace initiative that led to yesterday's face-to-face meeting between Duarte and guerrilla leaders.

They said the liberal group, acting outside the Reagan administration while informing it of its efforts, used the good relations its members have established with a relatively moderate faction within the Salvadoran armed forces and with rebel officials to help arrange a major prisoner exchange between the two sides announced earlier this month. Last spring, the group emphasized to the Army that further congressional aid to El Salvador depended on removing right-wing officers linked to death squads here.

Tsongas, who appeared in the northern town of La Palma yesterday on the occasion of the historic Duarte-rebel meeting, said today that he was not involved directly in Duarte's decision to offer the peace talks. However, he said he originally had been asked by both sides to play a role in the arrangements for the meeting.

Sources said that the work by the "Tsongas group" may have spurred Duarte into seizing the peace initiative and helped facilitate his decision by indicating that at least one faction of the Army would not oppose the open, direct talks.

"Duarte had talks because he wanted to," said Leonel Gomez, a Salvadoran exile in Washington who helped facilitate the Tsongas group's efforts. "We needed him as much as he needed us." Duarte's election last May, Gomez said, also helped persuade the military moderates to go ahead with the private talks.

Gomez, who was interviewed today in Washington, is a former official of the Salvadoran land reform program who fled the country following the January 1981 assassination of land reform head Rodolfo Viera. He has long been known to have extensive contacts among various key groups in the Salvadoran conflict.

Those talks apparently began, not as an effort to deal with the guerrillas on any level, but as an effort by one faction in the Salvadoran Army to seek assistance in reforming the corruption-ridden armed forces. Their interest was spurred, sources said, by the congressional testimony of a high-level Salvadoran military official last March on corruption and death squad activity.

The testimony by Salvadoran Army Col. Roberto Santivanez, the former head of the military's intelligence branch, was arranged by Gomez and Tsongas. According to Gomez, "Santivanez broke a logjam that had existed in the Salvadoran Army for years. He created openings and a willingness among some of the younger officers.

"They knew they were not going to survive if they did not do something about corruption." Through Gomez and others, contacts between other Salvadoran officers and Tsongas were arranged. They were well into the process, Gomez said, before the subject of expanding their talks to a possible prisoner exchange was broached.

Some factions of the guerrilla movement were skeptical, believing that anything that helped the Army "clean up its act" would undermine the overall leftist war effort, sources said. Others, however, saw the contacts as the beginning of a possible opening for wider talks.

As the talks leading to the prisoner exchange progressed this summer, sources said, the State Department was kept informed, but it did not show any interest in intervening. The White House, a congressional source involved in the effort said, "is so fanatically obsessed with Nicaragua, the Sandinistas and maintaining the covert war there, they didn't even pay any attention to it."

A key member of what eventually became the Tsongas group is retired U.S. Army Lt. Col. Edward King, who served in Latin America when he was on active duty and is acquainted with many Salvadoran officers. Other members of the group were said to be former U.S. ambassador to El Salvador Robert White and Rep. James Shannon (D-Mass.). Shannon and King also were in El Salvador for the La Palma meeting yesterday.

One of the group's most important contacts in the Salvadoran military is the chief of staff, Col. Adolfo Blandon, according to several sources. Blandon is widely regarded as the head of the relatively moderate faction of the armed forces.

Asked about his efforts, Tsongas said here today that he had been "involved" in some meetings in the mediation effort, but he declined to be specific.

"What Ed King and others did in the six or seven months before this is simply not going to be revealed," the senator said. "We don't think there's a role for us at this point, and we want to stay out of it."

Tsongas, accompanied by King, was interviewed at San Salvador's international airport early this morning before they flew to the United States. Tsongas had come here expecting possibly to accompany Salvadoran rebel civilian leaders Guillermo Ungo and Ruben Zamora on their road trip Sunday from the airport to La Palma -- thus providing a kind of security for them by his presence -- or to serve as a neutral witness inside the La Palma church where the talks took place, according to sources involved in the effort.

By the time Tsongas arrived Saturday, however, the Salvadoran government and the left had arranged for foreign diplomats to accompany Ungo and Zamora, and for Roman Catholic church leaders to serve as witnesses.

"We were invited down by both sides. We thought we had something to do down here. It turned out that what we were asked to do was resolved by the time we got here, and so we basically played a role of tourist down here," Tsongas said.

U.S. Ambassador Thomas Pickering, asked this morning about Tsongas's role, said: "I haven't seen him this time, but he is a man who has many close friends in El Salvador, and he has friends on both sides whom he sees.