WHEN PRESIDENT REAGAN began his trip to Latin America last week, he said he was going "with an open mind, to listen and to learn." But when he returned to Washington five days later. Reagan remained as set and predictable in his ways as he was before his departure. The President continues to see the region through a distorting East-West prism; countries are distinguished only by their allegiance to either capitalism or communism The real problems of Latin America--the social, economic and political inequities that affect different nations in different ways--continue to be ignored.

A tenuous case can be made that the Administration is taking a harder line on human rights excesses in El Salvador. But the White House's recent attempts to sell aims to the rightist regime in Guatemala and destabilize the leftist government in Nicaragua are telling signs of the President's dangerous mindset.

The Administration has been flirting with the Guatemala regime ever since General Efrain Rios Montt took power in a coup last spring. Reagan wants to end a four-year freeze on arms sales to that country imposed by then-President Carter because of serious human rights violations.

Rios Montt has done nothing to deserve the trust such a change in U.S. policy would indicate. New elections, promised by the Guatemalan leader, are still unsure, and terrorism--particularly from rightist death squads--continues to plague the country. Reagan's desire--announced during his trip--to send more guns to Guatemala would only make the situation worse

Also last spring, the White House denounced as untrue a story leaked to the press that Washington was financing paramilitary groups to topple Nicaragua's leftist regime. But the story resurfaced last month--and this time, Administration officials are privately not denying its validity.

The Administration is concerned with the significant Nicaraguan arms build-up. But the Sandinistas, whose repeated friendly overtures to the U.S. have been ignored, claim they need a bigger army to repel a U.S. or U.S.-sponsored invasion. When Administration officials admit that such plans are in the works, it isn't difficult to empathize with the Nicaraguans.

President Reagan wants to squeeze communism out of Latin America, a goal that even some liberals wouldn't dispute. But by pouring more guns into the area and putting undue pressure on already leftist regimes, the President is only helping to bring about the kind of radical left revolutions he so wants to avoid.