It is dawning on people that the tough case in Central America is El Salvador, not Nicaragua, and almost no one wants to take it on. It's too hard.

Nicaragua is tough because it's had a revolution. But paradoxically that's its potential saving grace too. The Nicaraguan people dispute the second, Sandinista revolution, but most of them accept the first, anti-Somoza one. Somewhere in between the first and second revolutions may lie terrain on which Nicaraguans can at least contend political-ly, even if they cannot reach harmony. This is the premise that current peace efforts are testing.

El Salvador is tough for precisely the opposite reason: it hasn't had a revolution. The power of the old feudal-military oligarchy has been clipped but not broken by the democratic tendency represented by President Jose Napoleon Duarte. Against that power stands a leftist movement with a not entirely mindless conviction that access to El Salvador's brand of democracy may lead to a dead end.

The Reagan administration needed a model in Central America and was easily drawnto the democratic dream and the heroismof the Duarte government. The administra-tion was right to conduct this sort of policy, and Congress was right to support it. I don't see how Americans could have done otherwise.

But though American policy has kept the Duarte government afloat and seen success by some measures, overall it has been a failure. A cruel guerrilla challenge persists, the people suffer, the economy is a wreck, and democracy probably could not survive American disengagement. For the first time in the history of U.S. foreign aid, aid to El Salvador this year ($608 million) exceeds a country's own contribution to its budget ($582 million).

Sen. Mark Hatfield (R-Ore.) and Reps. Jim Leach (R-Iowa) and George Miller (D-Calif.) cite this somber fact in their report to the congressional Arms Control and Foreign Policy Caucus titled ''Bankrolling Failure: United States Policy in El Salvador and the Urgent Need for Reform.'' Blaming the doubly em-battled Duarte government for most ofEl Salvador's woes and suggesting an aid squeeze in the name of reform, the report amounts to opening a second front against Salvador's frail democracy. It cannot be taken seriously.

But the report is a telling reminder that most of us have averted our gaze from the contradictions of El Salvador, either because we felt that Nicaragua, with its more evident overlay of East-West conflict, was more urgent, or because we hoped too simply that the virtue of Jose Napoleon Duarte would somehow reap its own reward.

Now the question arises whether the El Salvador struggle can be tamed in the context of a regional peace agreement designed in the first instance to put out the fire in Nicaragua. Not only is a revolution unmade in El Salvador, however. In Nicaragua both sides are vulnerable to outside pressures: precisely in the rigging of those pressures lie the possibilities of diplomacy. But in El Salvador, neither side is so vulnerable: the United States finds it hard to press (and to reform) an imperfect but struggling elected government, and the guerrillas are deeply rooted and sustain themselves internally to a considerable extent.

This is the bleakness supporting the notion that perhaps El Salvador can be bypassed, left to its own rages as some occupied islands were left behind in the American Pacific campaign of World War II. A despairing idea but not necessarily an unthinkable one.

Better to use the current surge in regional diplomacy to reinforce lagging efforts to make both sides in El Salvador reduce the terrible civilian toll. If it is too much to expect a settlement, it should not be too much to aspire to civilize somewhat the conduct of an unavoidable class war.

The more distant but still necessary hope that the Arias plan means to keep alive looks to the reconciliation of a country where not just classes are at war but families and perhaps individual psyches too. This is, I surmise, the basis on which church figures and appeals of religious community become relevant to a quest for peace led in its official aspect by secular politicians. Is it merely a bitter irony that the country's name is, to translate, "The Savior"?