Even presidents deserve fair treatment. But Ronald Reagan's critics in Congress and the media are seriously distorting the issues and the debate surrounding the Iran-contra matter.

Some critics have used the Gulf crisis and the Venice summit as occasions to argue mistakenly that the U.S. sale of arms to Iran was responsible for Kuwait's request for Soviet help, for Gulf states' reservations about pressing the war against Iran and for the allies' refusal to join in a stronger collective action to protect free navigation in the Gulf. Other critics insist on treating the Iran-contra issue as though it were manifestly a legal and constitutional question, rather than a political issue involving Democrats versus Republicans.

In both cases, these critics have escalated the debate far beyond the issues actually involved -- the sale of arms to Iran and the organization of support for the contras during the period of Boland Amendment prohibition. It now encompasses more the basic questions of foreign policy and law. As a result of this escalation, many are being misled not only about the Reagan administration and the issues, but, more seriously, about the world.

''It was not by coincidence,'' wrote one liberal columnist, ''that immediately after the news of the arms sales broke in November, Kuwait turned to Moscow for protection of its tankers in the Gulf.'' ''This faithless, doomed conspiracy,'' wrote a leading Democrat, ''has reached far beyond mere disgrace. It has threatened the balance of power.''

But none of this is true, and it is extraordinary that well-informed, sophisticated commentators should suggest -- and worse should believe -- that the U.S. arms sales had such effects. Regardless of how ill-conceived those sales were, they did not shock our allies, almost all of whom have sold or otherwise supplied weapons to Iran, Iraq or both. Some have even sold components for chemical weapons to one of the belligerents. And many have negotiated for release of hostages.

Quite different reasons explain the allies' refusal to join a joint action in the Gulf: the habitual dislike of collective action, reinforced by doubt that the situation requires such strong medicine and fear that international action by powers outside the region may make matters worse.

Other states in the Gulf were not shocked by the U.S. arms sales, nor is their reticence to pursue an all-out war against Iran caused by American policy. Ambivalence and ambiguity in foreign affairs, including Kuwait's request to the Soviets, are a regular characteristic of the complex politics of the region.

Let me be clear. I believe the arms deal with Iran was unwise because it was not appropriate for the United States to strengthen the Ayatollah Khomeini -- no matter how marginally. The arms-for-hostages deal was ill-conceived and conducted because it neither rescued the hostages nor punished their kidnappers. I believe, moreover, that the allies are probably correct in declining to join a more forceful, concerted action in the Gulf, there being a real risk that such action would spread rather than contain the conflict.

But let us conduct debate about these matters on their merits and criticize the policies on their demerits, rather than reinforce mistaken notions that U.S. actions cause almost everything that is wrong around the globe. We are not so powerful and other governments are not so readily influenced.

Modern American liberals are as reluctant to face unpleasant facts about other countries as they are to face the limits of U.S. power. The combination does not contribute to realism in the discussion of foreign policy.

Reagan's critics also distort the issues when they treat the debate about U.S. policy in Iran and Nicaragua as primarily a legal or constitutional struggle between two branches of government rather than a contest between Democrats and Republicans over who shall control foreign policy.

Treating the issue as constitutional rather than political implicitly depoliticizes a highly political struggle over Central American policy between the Democrats, who control Congress, and the Republicans, who occupy the White House. The administration is tacitly cast as suspect and Congress as defender of the law. Indeed, a great deal of what is written these days sounds as if Congress is made up of dispassionate members of a nonpartisan league for good government trying to control a band of lawbreakers.

It is clear that the administration went to great lengths to find support for the contras during that period when Democrats in Congress had succeeded in temporarily blocking aid. But, after months of hearings, it is not clear that any of the administration's actions were illegal.

The repeated suggestion by the media that laws were broken reflects a prosecutorial attitude toward what is essentially a political disagreement.

In fact, neither Ronald Reagan nor Congress is bound by the law or the Constitution to accept the other's interpretation of their powers. Whether the Boland Amendment was constitutional, or whether it was violated, are questions for the court. But there is no question at all that the Iran-contra debate is a red-hot political issue between Democrats and Republicans, and that its outcome will affect the future of Central America and control of the U.S. government in 1989.