THE CHANCE that El Salvador will not become a political issue seems to be fading. President Reagan, faced with a jittery Congress, has striven to put a bipartisan label on his policy, but at the same time he suggests that the Democrats, if they pinch off aid, might yet be held responsible for "losing" El Salvador. Prominent Democrats, meanwhile, are trying to tear off that bipartisan label. Former vice president Walter F. Mondale says the Reagan administration has upended the Carter emphasis on political and social reform and turned American policy into "principally a military venture"--one certain to lead, he declares, to the dispatch of American troops, notwithstanding Mr. Reagan's pledge to the contrary.

In fact, it is not a very illuminating argument. The president is right to say that if El Salvador is "lost" by Congress' overburdening aid with conditions, then those who laid on the extra burden will deserve to be held accountable. But that is not the only way disaster could befall El Salvador. It could also arrive as a result of a Reagan policy in which the war goes on, unsoftened by any prospect of a political solution. We have yet to hear the president say that if the bottom drops out of El Salvador, he is prepared to take the blame.

As for Mr. Mondale, one can appreciate why for political reasons he might want to detach the Carter administration, his party and his own presidential candidacy from the current policy, which is going poorly. This has led him, however, to a misstatement of what is going on.

It is not true that Mr. Reagan rejects "any kind of effort to bring about social and political reform." The Reagan commitment to reform can be measured in dollars (military aid is only a third of the total) and in the patent discontent of the hard right and its death squads. Nor is it true that the president "rejects negotiations." He rejects the kind that he fears might lead straight to a guerrilla takeover--we assume that Mr. Mondale does, too. The trick is to find an approach that will draw in the democratic left, slow the war and produce a generally acceptable result.

We grant that this is no easy task. Perhaps that is why one important initiative for a bipartisan policy in Central America, Sens. Henry Jackson's and Charles Mathias' call for yet another presidential commission, is focused on the region's "serious long- term problems of security, poverty, and democratic development." Meanwhile, the debate over short- term policy intensifies. Those who participate in it should be held to fairness and the facts.