Consider the impact of the Central American situation on U.S. politics as we move toward a presidential election year.

It is said that El Salvador is another Vietnam, that Vietnam was a vastly unpopular war, that the American people didn't support our actions in Vietnam, that they don't support our actions in Central America, and that Ronald Reagan is heading into a political as well as a military quagmire. It is said that Democrats, by opposing Reagan on Central America in Congress, will gain a political bonus.

Don't believe it. If the Democrats end up being seen as the party that makes it difficult or impossible for the United States to respond in Central America, it is entirely plausible, perhaps even likely, that Democrats in Congress will suffer and that Ronald Reagan will be re-elected in 1984 precisely on the wings of this allegedly unpopular issue.

Some attitudinal history: public opinion polls show that from the first day of the Vietnam War to the last, a majority of the American people basically supported the stated commitment of the sitting president to that war. That was true of Kennedy, Johnson, Nixon and Ford. A monumental study of the Vietnam War in 1980 by pollster Louis Harris revealed that 90 percent of the veterans who served in that war endorsed the statement, "Looking back, I'm glad I served my country."

Moreover, at the most intense point of the Vietnam War, roughly coincident with the 1968 presidential election in America, it was the somewhat hawkier candidate (Nixon) who beat the somewhat dovier candidate (Humphrey). If you factor in the presence of the even more hawkish third-party candidate (Wallace), that interpretation is made more credible. Still, it may have been accidental; there were extraneous factors. But what happened four years later was no electoral accident. That is why there was no President McGovern.

El Salvador, it is true, is not a popular cause in America today. We are not a bellicose people. Few Americans go around looking for trouble all over the world. But that is very different from saying that Americans won't support their president when he says, with some credibility, that America is threatened.

The biggest single reason that the American public has not been sensitized so far to the threat in Central America can be attributed to the mistakes of one man: Ronald Reagan. For two years he heeded aides who told the president to put this back-yard problem on the back burner in order to make a big political splash by cutting taxes. Dreadful advice--bad for the country, bad for the president.

But that has changed. The president's speech last week to the joint session of Congress could well have been the political turning point of his presidency. It said most of the obvious things that needed saying: that freedom is under threat next door, that if the communists are allowed to spread their fire in Central America the flames will lap at the United States, that if the United States doesn't act responsibly in Central America neither our friends nor our adversaries will take us very seriously anywhere in the world.

So much for substance. It was a moderate, conciliatory speech, well delivered. There was only one truly political sentence in it, but it was Himalayan in its long-term political meaning. Lest anyone missed it, it was the last sentence in the speech, just the place where the message is supposed to be. After sketching out what America must do, the president concluded: "Who among us would wish to bear responsibility for failing to meet our shared obligation?"

If the political potency of that sentence was lost upon the press, rest assured that Democrats on Capitol Hill heard it, and are brooding upon it. Who indeed, running for office, is prepared to bear the political responsibility for failing to meet the shared obligation to keep those flames from lapping at the United States?

In this speech at least, the president was low-key. (Perhaps because he was so tardy on this issue in trying to lead the country he's been elected to lead.) He didn't say that if Congress opposes him and dire things happen, there will be a "Who lost Central America?" debate in this country that will make the old "Who lost China?" debate look like a tea party. He didn't say that if the Democrats nickel-and-dime the president on this issue, handcuffing him in Central America, that there will once again be a big argument in this country about who's mushy on Marxism. He didn't say it, but he meant it . . . for all the forces of political gravity would take us exactly to that sort of an argument.

Unfortunately, Sen. Christopher Dodd of Connecticut advanced the likelihood of just such an argument in his official Democratic response to the president, carried by all three networks. His speech was demagogic and wrongheaded. More important, it was not an accurate reflection of the mainstream of the Democratic Party on this issue.

Dodd chose not to address the central question at hand: what do you do when people are shooting at you? He made no reference to continuing our military or economic aid to El Salvador.

One Capitol Hill observer estimates that only about a third of the congressional Democrats support the Dodd view of the Central American situation. Surely not all of the remaining two- thirds buy the whole of Reagan's position, but they are willing to engage in a constructive dialogue on the issue. Majority Leader Jim Wright said after the speeches that he was "absolutely, firmly and enthusiastically" behind the president on El Salvador. And he also questioned whether a Democratic "response" should have been delivered at all, because a prescheduled response presupposes disagreement.

If a major argument about Central America does surface in a Reagan-versus-the-Democrats fashion, who will win? This is a question that is of enormous importance to congressional Democrats who will face the voters in 1984 and most particularly important to the men who hope to run against Reagan for the presidency.

All those who-cares-about-Salvador attitudes could change very quickly. A massive but nonscientific ABC telephone poll (a third of a million people phoned in) after the president's speech revealed that 77 percent of the American public agreed that the Central American situation represented a threat to the United States. Anyone who thinks that in the post-Vietnam era America has turned pantywaist might do well to recall that most Americans would just as soon have sacked Iran only three years ago.

The presidential hopefuls should chew on some additional facts. Foreign policy has been a major issue in 10 of our last 11 presidential elections. In recent times we have never elected anyone dovier than a moderate hawk. And, as Zbigniew Brzezinski likes to point out, Democrats can win when they appear moderately tough (Roosevelt, Truman, Kennedy, Johnson and Carter in 1976) and lose when they don't appear that way (Stevenson, Humphrey, McGovern and Carter in 1980).

Moreover, pollsters seem to agree that even when foreign policy is not a huge issue in and of itself, it is a key way in which voters determine whether a candidate is in tune with "traditional American values." Voters are looking for a stand-up guy who won't be pushed all over the lot.

It seems fairly clear that after all the dust settles most of the Democrats in Congress will not shut down military or economic aid to Central America. They will develop a policy that tries to shape such aid with a somewhat different emphasis. They will do this for sev eral reasons. Most of them agree

that the United States must make a

stand. And most of them know that

they dare not risk a political shoot-

out with the president on this is-

sue, despite the current unpopu larity of the Central American situa tion.

The only question now is whether

the Democrats will go along with

grace and with constructive sugges tions--or with a mean-spiritedness

that can unravel so much progress

that has been made within the

Democratic Party in the last few

years on the issues of defense and

foreign policy. The Democrats spoke

with sense and hardheadedness on

the subject at their Philadelphia

mini-convention last year. Front-

runner Walter Mondale deserves

two cheers for his foreign and de fense policy speech a few days ago; it

showed that a liberal Democrat

could be both tough-minded and

critical of the president. Most other presidential hopefuls have also been able, so far, to stay out of the "Dovier-Than-Thou" syndrome that often afflicts Democrats involved in primaries.

The Democrats--the party and the presidential candidates--have two potential options. They can extend substantial cooperation to Reagan in Central America--offering ideas in a healthy spirit of bipartisanship. That will effectively neutralize it as a campaign issue. The Democrats then will have a good chance to go out and beat Reagan on other issues in 1984.

Or they can go into rhetorical opposition. If they do that, I believe they will risk losing the election to a Ronald Reagan who will charge all across the nation denouncing them as spineless.