For the millions of Salvadorans who could not accept President Jose Napoleon Duarte's invitation to attend talks with rebels today in the northern town of La Palma, participation in the one-day interlude of peace came via transistor radios and village televisions.

A brief and uneasy propaganda truce allowed the Salvadoran media to provide an unprecedented flood of information not only about the talks themselves, but from and about the leftists whose names and activities for years have been uttered only as oaths over the airwaves.

There is no official censorship in El Salvador, but years of activities by death squads have ensured a right-wing slant in all the local media. It is not so long ago that the appearance on the street of the mutilated corpse of a local reporter was a common event.

Nor have years of clandestine shortwave guerrilla broadcasts been a paragon of truth or balance. Normally they are confined to body counts, leftist harangues and recountings of the perfidy of the government and Army.

Today, however, propaganda took somewhat of a holiday in El Salvador's media. Suddenly, rebels who for years have been routinely referred to in official news broadcasts as los subversivos, or, with heavy irony, as los senores terroristas became "the ones who have taken up arms."

Radio reporters in La Palma freely interviewed radical priests from guerrilla-held zones and rebel leaders.

For its part, the left substituted its usual references to "puppet Duarte" with more respectful allusions to the talks between "the regime of Jose Napoleon Duarte" and themselves.

For the visitor to La Palma, yesterday's meeting provided the extraordinary spectacle of guerrillas and government security forces in civilian dress being escorted by adolescent Boy Scouts in khaki uniforms. For perhaps millions of Salvadorans who could not make the pilgrimage to La Palma but monitored the events on the radio the day held many surprises as well.

On the air, the guerrillas claimed that most of their weapons come from the United States and are captured or bought from the Salvadoran Army. Before a nationwide audience they said their field hospitals have treated the civilian victims of both phosphorus and napalm bombs.

The right of reporters to broadcast the views of both sides in the civil war was not won without a brief skirmish, however. When the first guerrilla interviews went on the air yesterday morning, the government put all radio stations on the national network. A short while later the decision was reversed, but throughout the day broadcast quality on some commercial radio stations declined sharply whenever a guerrilla representative was on the air.

The propaganda truce extended only partially to the other media. Television broadcasts referred to the guerrilla armies and their spokesmen by their proper names but did not transmit any interviews with the ubiquitous representatives of the left in La Palma.

The country's three daily newspapers range from right of center to extreme right. The most extreme of the three, Diario de Hoy, carried news of the meeting on the inside pages, along with a story claiming that "many sectors of the population were unhappy with the almost ceremonial reception given the subversive representatives" on their arrival in the country yesterday.

Last week, the afternoon daily El Mundo carried a full-page, paid advertisement for the right-wing National Republican Alliance of Roberto D'Aubuisson. The statement implies that Duarte's decision to hold talks with the rebels and the attention focused on the meeting by the international media are all part of an international Marxist plot.

For their part, the rebels did their utmost to take advantage of the information windfall represented by the meeting. News crews from the guerrillas' two shortwave radio stations mingled with the rest of the press corps in La Palma.

Guerrilla representatives not taking part in the bilateral talks inside the town's church granted interviews and read statements before whoever would listen. Both sides staged a "war of the walls," as well, plastering the town with slogans and counterslogans.