THERE IS, CONCEIVABLY, good news from El Salvador. It's reported that the guerrillas are ready to negotiate an end to the war. The bid comes from their No. 2, a woman who does not tell her name. She offered to talk with the very junta the guerrillas used to disdain as a negotiating partner when they demanded to deal directly with the United States. Warning that no one should think the offer was being made "because we are weak," she stated that if talks don't come "the war will deepen."

Do the guerrillas see the Reagan policy taking hold, and do they hope to make the best political deal available now, or at least to distract the junta and its foreign friends? Can they deepen the war? It would be foolish to condition a response to the guerrillas' proposal, if it's real, on a single reading of their motives. Nothing known of the guerrilla command, which is entirely unbeholden to its civilian political front, indicates it has the slightest interest in a pluralistic democratic solution. Its program is revolutionary dictatorship. But that is merely a reason to proceed carefully. The guerrillas no doubt have their own suspicions.

Until now, nothing stirred on the negotiating front. The guerrilla proposal to negotiate over the junta's head was a non-starter. President Duarte was ready to talk with the civilian opposition alone, but it refused. Assorted international interventions foundered. Is there now a real chance for direct talks? Any party that neglects even the remotest chance to end the slaughter takes on a heavy responsibility.

The guerrillas do not indicate they will improve the atmosphere by a cease-fire, so the junta will have to fight on. But unlike the guerrillas, the junta has a second front: elections. It is necessary to ask, as we have asked, whether these will be free and fair, but the answer is not to damn them in advance. It is, as Venezuela suggests, to improve them by guarantees, observers and anything else at hand.

The guerrilla command, thanks in part to Nicaragua and Cuba, is a formidable military force. But no serious observer pretends it enjoys any substantial popular support or political legitimacy. The junta's promise and partial delivery of reforms--the reforms that stole the guerrillas' thunder and led them to declare war on the junta--seem to have won it a broad measure of hesitant tolerance if not yet full-fledged support from the masses of people in the center. Its enemies are the extremists of left and, of course, right. The election process it intends to open in March can in time confer a true mandate. The best way to enter negotiations is to forge ahead with that process.