SAN SALVADOR, El Salvador--The rightist Republican Nationalist Alliance yesterday claimed victory over the governing centrists in a presidential vote leftist rebels tried to thwart with attacks launched across the country.

The military said six soldiers and 23 guerrillas were killed in clashes. In addition, security forces shot to death three journalists--two Salvadorans and a Dutchman.

Presidential candidate Alfredo Cristiani, a wealthy coffee grower, told reporters that his party's unofficial count showed him leading with 54 percent of Sunday's vote with about 75 percent of the ballots counted.

"We are sure and we proclaim ourselves the victors," Roberto D'Aubuisson, the founder of the rightist party known as Arena, said at a news conference yesterday.

The rebels claimed a low voter turnout--unofficially estimated at roughly 60 percent--rendered the results meaningless.

Their Farabundo Marti National Liberation Front had called for a boycott and launched widespread attacks to keep voters at home.

Unofficial reports by a television station, the U.S. Embassy and the leftist Democratic Convergence party indicated Arena had defeated the incumbent Christian Democrats.

Election officials had no results early today. They said they were having computer problems and suspended counting this morning. Guerrilla sabotage of electric power and telephone lines had hampered vote collection from provincial polling places.

A team of 21 U.S. observers said the vote appeared to have been fair, but one observer said violence had frightened many people away.

"There is no question that the intimidation of the [rebels] is working," said William Doherty, an AFLCIO official on the team.

U.S. Ambassador William Walker said a turnout of about 60 percent would be a defeat for the rebels.

Cristiani, 41, campaigned as a moderate, although he represented a party long associated with extremism. D'Aubuisson, a former army major who has for years denied charges that he is linked with right-wing death squads, has been at Cristiani's side throughout the campaign.

The Christian Democrats, their headquarters almost empty, said they would have no immediate comment on the returns.

U.S. policy in El Salvador has been aimed at shoring up a centrist government represented by the Christian Democrats and President Jose Napoleon Duarte, who is dying of liver cancer and leaves office June 1.

"The United States must recognize the will of Salvadorans," Cristiani said in a television interview Sunday night. He said he saw no reason "we can't have a relationship of mutual understanding."

Col. Rene Emilio Ponce, chairman of the joint chiefs of staff, said the armed forces "repelled what was in reality a nationwide offensive by the [rebels]."

But the Salvadoran Correspondents' Association, citing the deaths of the three journalists covering the vote, accused the military of intimidation. "In these three incidents, we note with alarm a tendency on the part of the armed forces that appears aimed at intimidating and frightening the press corps in order to make their work more difficult," the association said in a statement.

Ponce said a soldier had been arrested in one of the killings and the others were being investigated.