Serious people who know El Salvador insist that no negotiation is possible there. They see only trouble coming out of any effort to pursue talks. But other serious people who know El Salvador insist that a negotiation is conceivable. They are not sanguine, but they feel no stone should be left unturned to end the war.

So who's right?

It's the wrong question.

When a country is as desperate as El Salvador, it is unforgivable not to knock on every possible door. You must prepare for a variety of responses. But you must knock.

That is what is so disturbing about the administration's answer to the recent guerrilla bid for talks. "Nothing new," the State Department said, reaffirming its policy that opposition parties certified by the junta may compete in the elections scheduled for next March, if they accept the junta's terms, the principal one being to sever their connection with the guerrillas.

Connoisseurs of diplomatic nuance may wish to quibble over whether there was or was not something new. No sensible person would want to listen in. For it is a time to see if something can be started, and the way you do that is not to put on the old worn State Department phonograph record that says "nothing new." Instead, you consult our friends in the Salvadoran junta, and in the hemisphere, and work out some response that at least beckons the guerrillas and their political comrades into a further exchange.

Unprofessionalism aside, the only reason a diplomat should find himself saying "nothing new" to a negotiating bid from the other side is to signal that a political decision has been taken to avoid negotiations.

That does appear to be the case here. The administration seems to be placing all its bets on the junta's chosen elections route. This is not entirely frivolous. For considerations of domestic and international support as well as for considerations of intrinsic worthiness, it is good to emphasize a political solution.

This week at the Organization of American States meeting in St. Lucia, moreover, the administration won a substantial hemispheric vote of confidence. Most Latin and Caribbean governments are wary of the Cuban-Nicaraguan hand they see at work in El Salvador, and of guerrillas, and they apparently were gratified that the United States put aside its tendency to unilateral intervention and stressed a collectively supported political process.

The real test of the policy, however, is not whether other nations, for their own reasons, go along with it but whether it moves El Salvador toward a better place. A diplomatic triumph that leaves the country sinking into a swamp is a mirage.

Let us try to put gamesmanship aside and look at what the two sides in El Salvador actually have in mind when they talk about talks. What the guerrillas seem to want most, or first, is a dominant role for their military forces, on which, they believe--not without reason--their political power depends. What the junta wants is to detach the political opposition from the guerrillas, which would leave the opposition, or so it believes, at the junta's mercy. The junta sees the guerrillas' approach as the theft of power they cannot win in the field. The guerrillas see the junta's approach as a demand for surrender.

Both of them have a point. But the way to deal with this contradiction is not to throw up one's hands. It is to search for acceptable terrain in the middle. Perhaps there is none, or not enough. Salvadorans do sometimes seem so rigid, and divided, that good-willed mediation is a waste. For the United States and like- minded countries, however, there should be only one irreducible criterion: a settlement must reflect the will of the people of El Salvador.

Elections are the appropriate mechanism. But the elections contemplated in March will unavoidably be run by an army whose institutional history of disrespect for the people's will has been freshened recently by wholesale murders of the political opposition. No doubt such elections can be, and should be, improved by the presence of international observers. But a painful problem of public confidence will remain.

There is somber evidence that many guerrillas are anti-democratic at heart and maintain a hammerlock on many of their civilian associates. But if that is so, negotiations will show where the fault lies. A continuation of the Salvadoran tragedy can be justified only if the guerrillas leave no choice.