President Reagan's desire to intervene in El Salvador and Nicaragua has run into serious and widespread disapproval. It is probably fair to say that no foreign policy initiated at the White House since World War II has met such general scepticism and disapproval.
The measure of its unpopularity at home is provided by the current behavior of the opposition party in the Congress. The Democrats are sponsoring bills and resolutions which would attempt to prevent the President from sending not only United States troops but even American guns to the junta in El Salvador and to right wing movements among Nicaraguans.
The active opposition of the Democrats comes after reading current public opinon polls. Democrats do not lightly oppose policies which are labeled as being ''anticommunist.'' That makes any politician vulnerable to the charge of being ''soft on communism.'' In this case the Democrats have concluded from the polls that it is politically both safe and potentially profitable to oppose the Reagan policy on Central America.
Unpopularity of the policy overseas is equally general and vigorous. Not a single ally, not even the most loyal British, give approval and support. The French not only refrain from supporting, but even are deliberately and defiantly selling weapons to the revolutionary government in Nicaragua which Mr. Reagan calls ''Marxist.''
The Mexican government is publicly urging the President to change his policy, give up intervention in Central America with guns, and substitute a policy of attempted political reconciliation.
In spite of all this disapproval Mr. Reagan has undertaken a program of support for opposition forces in Nicaragua and is still sending American weapons to the ruling Junta in El Salvador. It is alleged, but not confirmed, that he has authorized the CIA to undertake a destabilization program in Nicaragua involving the blowing up of bridges.
Why does the President persist in a policy which is putting a strain on the alliance, which is unpopular in the country, which is being repudiated by a number of prominent Republicans in Congress, which well may be undermined in Congress, and which risks getting his party labeled as being the ''war party'' just in time for the November midterm elections?
If the political and economic trends of the moment persist until November, Republicans will go to the polls with the charge of being the party of both war and unemployment around their necks. Those are two heavy millstones for any party to shoulder in a midterm election. Why court both?
The clue to the reason for persisting in the militant policy toward Central America lies in the fact that whenever the President and his secretary of state talk about Central America they mention ''Marxism'' and identify the Cuban and Nicaraguan governments and the rebels in El Salvador with ''Marxism.'' They assume in their identification that any Marxist party, movement, or government belongs to the Soviet power system.
Thus, according to Reagan-Haig reasoning, the US must oppose Cuba, Nicaragua, and the rebels in El Salvador to prevent all three from becoming instruments of Soviet purpose in the Caribbean basin.
Here is where many part company from Mr. Reagan. They do not accept the equation of Marxism with instruments of Soviet purpose. None of the European allies makes the same equation which Mr. Reagan does - that a Marxist is automatically part of the Soviet system. Mexico rejects the theory. So do most diplomats the world around.
The evidence is heavily on the side of those who reject the Reagan equation.
The most populous country in the world is a Marxist country--China. It is in a more active state of hostility toward Moscow than is the US.
Yugoslavia is officially and publicly loyal to Marxism--although often deviating in practice. It broke with Moscow in 1948 and has been defiantly independent ever since.
The ''satellite'' countries of Eastern Europe would all get out from under Soviet influence if they could--except possibly Bulgaria. But if they did break away, would they also give up Marxism? Probably not all.
Cuba is definitely in the Soviet power system. In Cuba Marxism also means being an instrument of Soviet purpose. Much Washington thinking is influenced by this fact about Cuba. But worldwide there are more professing Marxists outside the Soviet system and even hostile to it than there are Marxists who bend the knee to Moscow. A billion Chinese Marxists dislike and fear the Soviet Union. It simply is not true that a Marxist automatically serves the Kremlin. Moscow must wish fervently that the Reagan assumption were true.