An outbreak of politically related murders and bitter partisan infighting has raised tensions here at the opening of El Salvador's two-month legislative election campaign.

The atmosphere has sharpened basic political divisions between President Jose Napoleon Duarte and his right-wing opposition, leading to predictions from his aides and church mediators that the next round of talks with leftist guerrilla leaders may have to be delayed pending the assembly vote.

One fear among political observers and some of Duarte's aides is that the recent assassinations in provincial towns and the climate of political confrontation in the legislature could crystallize doubts in the armed forces about the president's efforts at dialogue with the insurgents.

The military, under Defense Minister Carlos Eugenio Vides Casanova, publicly has blessed Duarte's attempt on the condition that he adhere to the constitution drawn up over the last two years by an assembly dominated by the right wing. But some officers have voiced reservations in private about the wisdom of talking with the rebels at a time when the Army seems to have the initiative militarily.

Msgr. Gregorio Rosa Chavez, the auxiliary bishop of San Salvador involved in mediation for the dialogue, appeared to be referring to this when he told reporters today that "internal conflicts within the government" have dimmed chances for an early third round of talks.

Archbishop Arturo Rivera y Damas, the main intermediary between Duarte and the rebels, had said last month that the next session was likely before the end of January. The first formal contact, widely hailed as a breakthrough in five years of civil war, was held Oct. 15 in the hill town of La Palma. A second meeting, during which the initial euphoria sagged, occurred Nov. 30 at a seminary in Ayagualo, nine miles south of the capital.

In that gathering, the guerrillas' Farabundo Marti National Liberation Front and their political branch, the Democratic Revolutionary Front, presented demands that implied substantial change in the constitution, including power sharing before new elections.

As a result, dialogue with the rebels appeared to have faded as a political selling point for Duarte's Christian Democratic Party by the time the election campaign for mayors and Legislative Assembly members opened Thursday. In addition, right-wing criticism of the contacts appeared to gain momentum.

Against this background, three municipal officials of the two main right-wing parties, the Nationalist Republican Alliance (Arena) and the National Conciliation Party, were killed in the two weeks leading up to the campaign. A fourth was slain Friday, a 29-year-old woman mayor.

An anonymous caller to a radio station claimed one of the killings for the Farabundo Marti National Liberation Front, declaring the victim was organizing rightist paramilitary squads. A second victim was found with a sign beside his body reading: "Because he was repressive with the working class."

Although authorities have not found the killers, the assassinations have contributed to the political acrimony. In addition, the secretary general of an agricultural association linked with Duarte's Christian Democrats was wounded in an apparent assassination attempt Jan. 14, and one of Duarte's aides, Pedro Rene Yanes, was killed Jan. 6 by an Arena member with whom he had a longstanding political rivalry.

"This is a product of the culture of terror," Duarte said then. "There is in people's minds a permanent hatred, a spirit of terrorism, of death. They believe they can reach solutions simply by assassinating and killing."

Msgr. Rosa Chavez, noting the political campaign in his sermon at the capital's main cathedral, deplored the most recent killings, the latest of thousands of similar slayings in El Salvador's recent history.

"All this is happening in a climate of much violence that already has cost the lives of citizens dedicated to public life. Once again, we must shout that violence does not lead to peace. Let us understand this before it is too late."

At the same time, Duarte has become embroiled in a constitutional dispute in the Legislative Assembly that has led some right-wing political leaders to demand postponement of the elections, now set for March 17. The confrontation has gone before the Supreme Court, and it is not known when a decision will be handed down.

The clash involves Duarte's veto of two sections of an electoral code passed over his objections by the assembly. One section would have prevented his son, Alejandro, from running for reelection as mayor of San Salvador. The other would allow Arena and the National Conciliation Party to run as a coalition but with their candidates listed separately on the ballot. This, the Christian Democrats contended, would give them an unfair advantage with the often illiterate voters.