The American people cannot but be deeply concerned about the course of events in Central America. The murder of the deputy commander of the US military advisers in El Salvador is but the latest tragic reminder of the risks which accompany direct United States military involvement there. The slaying of the first American serviceman will not weaken the Reagan administration's resolve to help the Salvadorean government in its war against leftist guerrillas. But it is certain to quicken public debate about whether US policy is being conducted as wisely as it can and should be.
The essential issue is the administration's focus on military operations - instead of on regional initiatives, political negotiation, and economic aid. President Reagan tried to strike a better balance in his recent speech on Central America. But echoes from the White House since then seem to belie any significant change of attitude. Now comes the news, for instance, that the US is tripling the number of US military advisers in Honduras and opening a training base there for Salvadorean soldiers - a plan that goes against the policy guidelines laid down by the Senate Foreign Relations Committee. The sudden replacement of Thomas Enders, the top US diplomat involved with Central America may also signal a toughening military posture.
It is time that US Secretary of State George Shultz took a stern hand in the situation and helped evolve a policy commanding bipartisan support. Remembering the anguish and divisiveness among Americans that flowed from the Vietnam war - and the political cost of that strife - every effort should be made to avoid domestic confrontation and to work together on what admittedly is a difficult problem on America's doorstep.
The point is that a military solution is not possible. It is in theory, perhaps, but a military victory against leftist revolution in Central America would require such a massive and continuing commitment of US military personnel and aid as to be insupportable politically. And, even if such aid were possible , it is not clear that a US-supported military victory would end up being perceived in Latin America as anything but another effort of ''Yankee imperialism'' to impose its will and stem the tide of social change.
What should the US do? Several things:
* Certainly not abandon a reasonable level of military aid to the Salvadorean government (linked to performance on human rights) or lawful efforts to interdict military supplies to the guerrillas. The Marxists should not be allowed to shoot their way into power. But, as many experts on the region as well as legislators on the Hill argue, the aim of the assistance should be to enable the Salvadorean government to survive so that it can negotiate - and negotiate effectively. The guerrillas must know that the US is behind the democratic process.
* The US can support regional efforts at negotiation, namely, the initiative being promoted by the so-called Contadora group, including Mexico, Colombia, Venezuela, and Panama. This group now seeks the cooperation of five other Latin American nations in initiating peace talks between Nicaragua and Honduras. Is it not logical that the countries closest to and most directly affected by the turmoil in Central America take the lead in dealing with their common threat? As a group of prominent US and Latin American citizens stated in its recent report:
''These countries are well positioned to play such a role, for they enjoy good relations with the countries of Central America and with the United States, and most of them have relations with Cuba. They have an urgent interest in ending Central America's tragedy, and they have the confidence of the relevant actors. The United States should make it clear that it favors and encourages an active role by the Contadora group in seeking an end to the Central American conflict, and that it stands ready to join the discussions as may be appropriate.''
* Economic aid should loom larger than it has. In the face of a fragile US recovery from recession, this may not be the right time to propose a massive ''Marshall Plan'' for El Salvador and other nations. But why not accompany strong US backing for a regionally negotiated settlement with a tacit promise of economic help once the war is over and peace returns? Such a generous offer - based on an awareness that Central America's problems stem in some measure from past US economic neglect and misguided policy - might serve as an inducement to negotiation. (Negotiation, it might be added, not with the Marxist extremists who indeed seek to impose a Cuban-style order on the region but with those responsible elements among the guerrillas who want to build a democratic order.)
Whether it is ''too late'' to save Central America from a Marxist tide is now the subject of much discussion and hand-wringing. It need not be. Not if Mr. Shultz brings his demonstrated diplomatic skills and instincts to bear on the problem - and not if the United States is prepared to make a long-term, sustained commitment to political and economic progress.