Between President Reagan's principal foreign policy problem and his No. 1 domestic concern there is what poet William Blake would have called "a fearful symmetry." The solution in each case suggests action he has pledged not to take.

He is wrestling with the question of how to reduce the deficit without raising taxes, a step he said would be taken over his dead body.

And in Nicaragua, he must accomplish his unavowed goal of toppling a Marxist regime without actually sending in U.S. troops to do the job the Central Intelligence Agency obviously cannot do with the "contras."

Only Minnesota and the District of Columbia denied Reagan the mandate to do whatever he wants to do. But he would be embarrassed to impose new taxes so soon after his campaign protests; and he seems to understand that the massive indulgence extended to him by the electorate stops short of dipatching GIs to a jungle war.

With taxes, he is obviously hoping that the Democrats will come to his aid. The way to go would be one of those "bipartisan commissions" that have so generously pulled his chestnuts out of the fire in the past. But the House Democratic leadership, burned by memories of helping out and then being blamed, is, for now at least, saying "not on your life."

With Nicaragua, Reagan could seek a nonviolent way out through the Contadora Group, which has been promoting regional negotiations. While giving lip service to the idea, the Reagan administration criticizes everything but the quality of the paper on which the draft terms are written.

Reagan's not-so-secret war is having the opposite effect on the country. Disaffection with the Sandinistas is evident. Junta leader Daniel Ortega won only 63 percent of the vote in an uncontested election. There is resistance to the draft; there is economic hardship. The Roman Catholic Church is vocal in its opposition to the Marxist character of the government. The promises of the revolution have yet to be kept. Still, the threats of the world's greatest military power have unified the country against the "gringos."

The flap over crates that were supposed to contain Soviet MiGs -- and didn't -- showed that the hysteria over another Cuba is not limited to Reagan and the right wing. Some liberals in Congress shouted that if there were MiGs, they must be bombed. Walter F. Mondale's assertion that under certain circumstances, he would "quarantine" Nicaragua shows how deep-seated is the fear of being thought soft on a communist stronghold in the hemisphere.

The administration continues to rail against the "military buildup" in Nicaragua, which raises the interesting question of what a small, poor country is supposed to do when informed that Uncle Sam is after it. Should its people put lillies on their chests, defend themselves with slingshots? The United States is playing the bully: moves toward self-defense will be interpreted as provocation.

The flimsy cover on Reagan's insistence that he wants not to overthrow the government but to make it more democratic is in shreds. The mining of the harbors of Nicaragua, the publication of a CIA manual -- a blueprint for terrorism that gave instructions on assassination -- could hardly be interpreted as innocent efforts toward a pluralistic society.

Reagan used strikingly different means of encouraging another Latin American regime to do right. General Augusto Pinochet who has a record of savage repression has recently begun a new crackdown that seems aimed at putting the whole country in jail.

Pinochet struck on our Election Day. The Reagan administration made the appropriate sounds of extreme displeasure -- then voted in the Inter-American Development Bank for a $35.7 million loan to Chile. The familiar Reagan rationalization for petting right-wing tyrants came from our ambassador: Banning aid would be "counterproductive to efforts to moderate Pinochet's course."

Reagan might find inspiration in President Richard M. Nixon's handling of Chile in 1970. His CIA helped overthrow the government of Salvador Allende and put Pinochet in power through a campaign of encouraging strikes, withholding loans and "making the economy scream."

Nicaragua is vulnerable. The heat of U.S. threats, the miserable contra raids, disrupt the economy and make the people nervous. Reagan says he merely wants to "squeeze" the Sandinistas. But he may strangle them economically. It would be less messy, although less macho, than sending in the 82nd Airborne.