The American military is saying it should not be ordered to intervene directly in El Salvador unless the American people are serious about letting it do the job right. There is widespread deference to this view. Almost everyone thinks, a bit guiltily, of the military's frustrations in Vietnam and nods in assent at its current qualms.

But wait a minute. What is this business about being serious? Why is only the military allowed to be serious in this regard? I do not recall anyone saying earlier that we should not intervene in El Salvador, by other than direct military means, unless we were serious. On the contrary, most people agreed it was Okay to intervene gradually, by relatively small increments of advice and aid, unseriously. The idea of doing as little as necessary was widely backed. That's how we got where we are.

Where we are is stuck: doing too little to carry forward our stated goals or even to prevent a certain erosion, and unable to muster the popular will to do more. It is a case of not having our cake, and not eating it too.

True, it has to be said for our Salvador policy that it reflects the popular mood or, to be precise, the popular ambivalence. It is a great if largely unhailed achievement of the legislative veto that it gave the public through Congress an unprecedented instrument for fine-tuning those aspects of foreign policy that hinge on money, as our policy in El Salvador has.

The other thing that has to be said about our policy is that it is not working well. So much for the comforting notion that what results from a thorough public immersion and debate, and from a collaboration between Congress and the executive--we have had both on Salvador--is a wise, sound and effective policy. The only consolation is that so far it has produced neither a larger Americanized war nor a collapse into a victory for the left.

Denying the first possibility and fearing the second, President Reagan attacked the dilemma laterally in his big policy speech in April. To stir a reluctant Congress to provide more aid, he drew a deep breath and pronounced both the country and the outcome there vital. At the same time, to calm a Congress alarmed by thoughts of military intervention, he promised to send no American troops. The contradiction between escalating the stakes and crimping the resources has since struck most people as painful but unavoidable--a legacy of Vietnam.

Many people believe, nonetheless, that the contradiction cannot be sustained and that Reagan will yet be driven to send in American troops--under the restrictions that American military men say they cannot abide. They say this because they think the bottom is falling out in El Salvador and they have no confidence that Reagan is moving to a negotiated settlement.

It is a fair question whether Reagan has an interest in the sort of negotiation--if one exists--with a fair chance of ending the war on terms minimally acceptable to both sides. Many of the doubters, though, fail to grasp that their own reservations contribute just as much as the president's skepticism to the poor current prospects of a negotiation.

The doubters keep holding up full transfusions of aid and tying on conditions. The Salvadoran guerrillas, seeing this squeeze, are sorely tempted to lay back and wait for the American opposition to saw off the Salvadoran government. They would be stupid not to see how much they can get for free.

If the doubters are serious, in other words, they will think again about what they want to accomplish in El Salvador. There is a limit to what can be done--in reforms, in human rights, in negotiations--by tightness on aid, since past a point a Salvadoran government cannot deliver on these difficult things if it is being ordered about by the gringos.

Generosity on aid is the formula for accomplishing something, if the something is carefully limited and defined. I would argue that that what we should want first in El Salvador is not rights or reforms but the end of the war on terms that both sides think they can live with. Therefore we should furnish the Salvadoran government decent aid, point it toward negotiations and shove.

I can hear you saying that Reagan will take the aid and let the Salvadoran army run. The proper response to that, if you really care, is not to make the Salvadorans pay the price of the argument among Americans but to throw out Reagan.