Top congressional leaders are to confer this morning with Secretary of State Alexander M. Haig Jr. about U.S. concern over alleged communist assistance for the leftist guerrillas in the El Salvador civil war, informed sources said yesterday.

Although the sources did not identify the congressmen, they said about eight were expected for the briefing by Haig and other department officials.

The Reagan administration, concerned that Cuban President Fidel Castro is masterminding the guerrilla offensive in El Salvador, is preparing to increase U.S. military and economic assistance there. And it is readying a campaign to publicize its information about the alleged flow of arms to the guerrillas from Cuba through neighboring Nicaragua.

The sources also said a team of State Department officials headed by Lawrence S. Eagleburger, who is to be assistant secretary for European affairs, left Sunday night to brief U.S. allies in northern and central Europe on the arms flow intelligence.

The sources added that two other teams were scheduled to leave last night or today on overseas briefing missions. One, headed by Lt. Gen. Vernon D. Walters, former deputy director of the Central Intelligence Agency, will visit Latin American countries; the other, headed by Luigi Einaudi, the State Department's Latin American policy planning chief, will go to southern Europe.

These missions are intended to counteract pressure in several Latin American and west European countries for support of the guerrillas and opposition to the military-civilian coalition ruling El Salvador on grounds it has abetted massive human rights violations.

Meanwhile, an FBI investigation has turned up evidence that might implicate El Salvador security forces in the murder of four American women, but Salvadoran officials have not cooperated with the inquiry, Time magazine reported.

The Carter administration cut off aid to El Salvador after the four women, three nuns and a lay religious worker, were found dead late last year.

In its Feb. 23 issue, Time reports that the bodies of two of the nuns were exhumed in the United States after Salvadoran doctors refused to perform autopsies. The tests showed the bullets that killed them came from the same kind of high-powered rifle regularly used by the security forces, Time reported.

A team of FBI agents was dispatched to help a four-member Salvadoran commission of inquiry.

Sixteen sets of fingerprints were lifted from the burned paint of the microbus the four women were driving the night they were killed, the FBI said.

Salvadoran authorities established the names of about 20 members of the national police troops and treasury police who were in the area where the women were killed, but their fingerprints were not compared with those found on the bus. Tests were not performed to determine whether their weapons fired the fatal bullets, Time said.

The microbus bore a smear of red paint where it apparently had scraped against another vehicle. Residents reported seeing the microbus being towed by a red vehicle, Time said.

Although financial aid to El Salvador was to have been suspended until a complete investigation of the murders was undertaken, the United States restored $10 million in aid to the country last month. One reason cited for the resumption was a State Department report of "progress" in the investigation.