The assassination of Salvadoran Archbishop Oscar Romero five years ago was carried out by former Nicaraguan national guardsmen directed by Col. Ricardo Lau, who later became chief of intelligence for the CIA-backed rebels fighting against the Sandinista government, a former Salvadoran security official charged yesterday.

Col. Roberto Santivanez, who was head of El Salvador's central intelligence agency in 1978-79, said at a Washington news conference that Lau had been paid $120,000 in connection with Romero's assassination by wealthy Salvadoran exiles on March 27, 1980, three days after the killing.

The killing of Romero, who was among the most popular and important figures in El Salvador at the time, was a key event in polarizing the political situation in that country. Salvadoran President Jose Napoleon Duarte has said the government is investigating the widely discussed crime, but no results of the investigation have been announced.

Santivanez gave interviews to several news organizations and about two dozen members of Congress a year ago recounting his inside knowledge of death squad activity in El Salvador, but at the time insisted that his name not be used for fear of reprisals.

His revelations caused an immediate stir even without use of his name.

There was a further stir when it was learned that Santivanez had been promised $50,000 as living expenses by critics of U.S. policy in Central America.

Bruce Cameron, a former congressional aide who helped arrange Santivanez's original testimony, said he actually received $32,500. Santivanez said yesterday that "money was not my motivation" but that funds were essential to support his life and travel.

The news conference yesterday, sponsored by an independent filmmaker who is releasing a documentary on Santivanez, came as the administration is preparing a large-scale effort to persuade Congress to reverse its cutoff of secret funding for the anti-Sandinista insurgents.

Beyond his charge against Lau -- which was not mentioned in his remarks last year -- Santivanez's news conference was notable for its description of the links between various Central American rightist officials and groups in connection with the Salvadoran death squads.

According to Santivanez, the decision to kill the archbishop was made by Miami-based Salvadoran capitalists "who gave the money" and was passed along inside El Salvador by Roberto D'Aubuisson, a former major in the security service who has since become a prominent figure in Salvadoran politics.

The killing was planned in Guatemala, according to Santivanez, and carried out by "two ex-Somoza Nicaragua national guardsmen working with a Salvadoran National Guard team."

Santivanez did not name Lau, who had been an intelligence officer and field commander for former Nicaraguan president Anastasio Somoza, as one of the archbishop's killers.

Santivanez said that, on the basis of a captured "diary" of death squad activity and "several other sources," Lau played "a key role" in training the death squads and was paid for Romero's assassination.

Lau was later chief of intelligence for the "September 15 Legion," one of the earliest paramilitary organizations fighting against the leftist Sandinista government that took over Nicaragua after Somoza's fall.

After the formation in August 1981 of the Democratic Front of Nicaragua (FDN), the umbrella group for the anti-Sandinista fight, Lau was its first chief of intelligence.

Secret Central Intelligence Agency support for the FDN and other elements of the "secret war" against the Sandinistas was authorized by President Reagan in November 1981.

Lau was forced out of the FDN intelligence post about September 1982, reportedly on CIA instructions, but has been described as taking an unofficial role in FDN counterintelligence as late as last year.

Bosco Matamoros, Washington representative of the FDN, said Lau at present has "no connection in any capacity" with the anti-Sandinista organization.

Matamoros said "we have no knowledge" that Lau had a role in the assassination of Romero, an act which Matamoros described as "condemnable."

Santivanez was removed from his post as chief of the Salvadoran national intelligence agency, ANSESAL, as a result of the October 1979 coup that brought a reformist group of military officers to power. In the following months, including the period of Romero's assassination, Santivanez was residing in Guatemala, where he said the assassination was planned.

Guatemala had been a haven for right-wing exiles following the fall of Somoza in July 1979 and the reformist coup in El Salvador in October that year. Santivanez said he had spoken at the time with hired assassins who made frequent flights from Guatemala into El Salvador to kill people selected for assassination.