IT WAS an inadequate defense of his Central America policy that President Reagan gave on Tuesday evening. Meaning, no doubt, to soothe public opinion, he pretended that the new American military maneuvers are routine. Baloney. Jeane Kirkpatrick put it straight the same day, saying the latest operations were a response to a Soviet-bloc military buildup in the region. If it's true, the president should say so.

Mr. Reagan gave only a hint of the best argument for showing American power: to help negotiations. A whole school is forming, mostly in the ranks of the Democrats, holding that force is one thing and diplomacy another. This is silly. Force or the threat of it, properly applied, can be one element of effective diplomacy. At a time when Congress is trying to dismantle those instruments of administration policy it can get its hands on, it is not surprising that Mr. Reagan turns to those harder for Congress to reach. Nicaragua has recently responded to the Reagan program by announcing an openness to a negotiating format and agenda more acceptable to the United States. Cuba is sounding more cautious. This is progress.

There is, of course, another element--a crucial one --of effective diplomacy: the harnessing of appropriate means to appropriate ends, that is, balance. It is a fact that the president has aroused a widespread suspicion that he is not using American power wisely or well. The Central America questions at his Tuesday news conference all reflected this skepticism. Many people feel either that he is bruising for a fight for unworthy purposes or that he refuses to put reasonable bargaining objectives on the table. It is unreasonable to ask the Salvadoran left to enter elections run by the undisciplined official armed forces. It is also unreasonable to insist that the American-sponsored invasion of Nicaragua go on until the current Sandinista government reforms itself internally.

We think that it is essential to convert any advantage gained by Mr. Reagan's military moves into bargaining coin, and that this can best be done under the auspices of the Latins' own Contadora initiative. But there is nothing automatic about the process. Too many of Mr. Reagan's critics utter "Contadora" and "negotiations" as though ritual incantation could turn hope into truth. They would do better to accept an obligation to define what they mean. Are the Contadora nations, Mexico in particular, ready to address legitimate American as well as leftist Latin concerns? Their successful diplomatic intervention is devoutly to be desired, if it produces a result better than a widening war on the one hand and a widening Marxist advance on the other.