SAN SALVADOR, NOV. 25 -- El Salvador's recently returned leftist political leaders issued a six-point program today as rightist leader Roberto d'Aubuisson, implicated in the 1980 murder of archbishop Oscar Arnulfo Romero, repeated his charge that a close military supporter of President Jose Napoleon Duarte was responsible for the killing.

The leftist political program contained little new, but the open proselytizing by the leftists, associates of the Salvadoran guerrillas, is making the conservative armed forces uneasy, according to military and government sources.

Officials and diplomats said the latest round of accusations and stepped-up leftist activities would heighten tensions. Some expressed fear of new violence, since both the far right and far left in the past have killed those they viewed as threats.

In a packed press conference, d'Aubuisson, 43, charged the Duarte government with treason and with wanting to kill him. Duarte narrowly defeated d'Aubuisson in the 1984 presidential elections and the two have long been enemies.

On Monday, Duarte made public the testimony of Amado Garay, who said he drove the getaway car for the assassin of archbishop Romero, an outspoken critic of the military, as he was saying mass in a chapel. His death helped fan the flames of insurrection into civil war.

Garay's testimony said d'Aubuisson, a cashiered National Guard major, ordered the killing and that Alvaro Saravia, then an Air Force captain, was involved in carrying it out. Saravia was arrested yesterday in Miami, and Duarte said today he had officially begun extradition proceedings.

Garay said Saravia went to see d'Aubuisson three days after the murder to report on the action. Today, d'Aubuisson said he was in Guatemala that day, having left the country the day after the assassination because he felt his life was endangered.

"They are throwing up this smoke screen to defend Col. Reynaldo Lopez Nuila, at that time commander of the National Police," d'Aubuisson said. "He is directly responsible not only for this death, but of many other more nefarious actions of the 1980s that were blamed on the death squads. Lopez Nuila is Duarte's golden boy."

Lopez Nuila, Duarte's closest military ally, is now vice minister for public security. He is disliked by fellow officers, who have pressed for his removal.

In the late 1970s and early 1980s death squads, often linked to the far right and operating out of the security forces, carried out thousands of political murders. This was one of the first times a former officer formally charged them with the killings.

"There were deaths, of course there were, and now I am categorical in saying it was the security forces that acted in those circumstances," d'Aubuisson said. "There was great disorder, great uncertainty, and there was no leadership in the Army, and many troops and officers took things into their own hands."

Duarte told reporters today: "Lopez Nuila is one of the best men in the Army. He has chased and captured criminals, and he has all my support. When this is over, no one will doubt that d'Aubuisson was the one intellectually responsible for the murder of Romero."

Leftist leaders Ruben Zamora, who returned Saturday, and Guillermo Ungo, who returned Monday, presented their political platform to several thousand cheering supporters at the National University.

Zamora said the solution to the nation's war was to join as many political forces as possible. "No single force can bring about a solution excluding the other forces," he said. "We need a convergence, a coalition of forces, excluding none but those that exclude themselves."

Under the left's plan, the first step would be to form a government of national consensus, in which rebels, unions, the business community and parties would be represented. Duarte has said the government is legitimately constituted and the guerrillas and their supporters must work within the existing framework.