Five revolutionary political leaders were buried in the battered cathedral of El Salvador's capital today before a small, panicky crowd.

The ceremony for the prominent leftists, abducted and killed last week by a right-wing death squad, was to have been an occasion for the revolutionary movement here to demonstrate what it claims is massive support among the Salvadoran people.

A year ago the organizations represented now in the Revolutionary Democratic Front were able to muster 100,000 people to march through the city, often at the risk of their lives. Today, only about 1,500 turned out to watch the service, and many of them seemed only curious bystanders.

As late as 8:30 this morning, Marco Portillo, provisional replacement for the slain Juan Chacon as representative of the militant Revolutionary Popular Bloc on the front's directorate, was predicting as many as 150,000 mourners. He said 50,000 had come earlier to see the bodies of the five leaders and one young follower lying in state and "thousands and thousands" would attend the funeral.

Afterward Eduardo Calles, who took the place of murdered businessman Enrique Alvarez on the front directorate, said the low turnout was expected. "The people are definately were put on notice that there were plans to massacre them," said Calles. "We didn't really expect many. We don't want to open people up to a massacre like that. The people have to focus now on other forms of struggle."

One other form that is increasingly evident is outright guerrilla warfare against the government. But one of the claims on which the reolutionary front has based much of its efforts to gain international support is that "mass organizations" in this country of 4.8 million population gave it extensive backing.

When Mexico hinted earlier this year that it might break relations with the U.S.-backed junta here, the Mexican foreign minister pointed to the popular support of the revolutionary movement as a key factor in whatever his government decided to do.

For at least eight months, that support has not been evident.Mexico recently agreed to support the junta, at least tacitly, by supporting it with oil.

Fear was a major factor in the low turnout today, however. The right-wing death squads that operate here with virtual immunity from government sanctions have become increasingly brazen. After kidnaping the leaders of the revolutionary front last Thursday and killing, extreme rightists bombed the cathedral where the bodies lay. The mangled wreckage of the car that carried the explosives was still in front of the cathedral this morning.

This same cathedral square has often been littered with bodies. In May 1979 national police, then under the rule of general Carlos Humberto Romero, opened fire on a small leftist demonstration and killed 22 people scrabling up the church steps.

Last March the funeral of assassinated archbishop Oscar A. Romero (not related to the general) turned into a bloodbath. More than 30 people in the crowd of 50,000 died.

Twice during today's services panic spread through the crowd and mourners sprinted for shelter. The young "self-defense" squads of the left -- some of them children of 10 or 12, few older than 20 -- broke out automatic rifles and hurled a few Molotov cocktails.

But the crowd soon realized that the panic was unfounded and most returned to conclude the service on the cathedral steps. After the six bodies had been walled into the cathedral's subterranean crypts and most people had departed, some shots were heard in the distance.

Then the young revolutionaries really cut loose. Openly brandishing guns, they looted and burned four trucks they had hijacked and used to block the entrances to the cathedral square.

For several minutes furniture from a moving van, sugar sacks from another truck and pharmaceuticals from a third could be seen making their way through the streets on the shoulders of looters. The Salvadoran armed forces, to avoid a bloody confrontation, stayed out of sight.

Tension is still palpable. The extreme right, according to Christian Democratic junta member Napoleon Duarte in a televised speech last night, is still trying to take over the government to attempt an exclusively military solution to to the threat of the left while ignoring the vast social, political and economic problems that spawned the guerrilla movement.

As one diplomat put it, there is an "extended coup" in the works that seeks to force out more liberal members of the government without resorting to direct armed confrontation. The terrorism of the last week, the diplomat said, is part of that process.

Although the left appears to have shown political weakness by failing to demonstrate major support today, the polarizaation and violence here continue.

In Mexico City, U.S. Ambassador Julian Nava confirmed press reports that he had attributed a role by Salvadoran soldiers in the killing of the political leaders. In a telephone interview, Nava said that he told Mexican journalists, "It appears, although there was doubt about it before, that junta troops were involved in the assassinations . . . However, we do not know for sure whether the assassinations were ordered by the junta or simply actions taken by soldiers associated with the junta."

[Nava said he based his observations solely on press reports from San Salvador. Asked to comment on the Salvadoran government's denial of any role, Nava said, "We have no reason but to take their denial at face value," although there were reports to the contrry. He added that in view of the U.S. commitment to the junta, he hoped it would prove not to have been involved.]