President Reagan's decision to sell five AWACS planes to Saudi Arabia presents complex and delicate issues of foreign policy and national security. The balance he struck is a close one, which 51 senators and 218 members of the House could reasonably resolve the opposite way.

The closeness of the judgment is precisely why Congress ought to go along with the president's decision. For it is plain as day that once the president agreed to make the sale, the worst possible outcome for American foreign policy and national security would be for Congress to reverse him.

A congressional veto would be bad for practical political reasons. It would probably be unconstitutional as well. All recent presidents and attorneys general have challenged the constitutionality of congressional vetoes, and the issue may soon be resolved in a case now before the Supreme Court. But Congress will have to make its AWACS decision before that happens, and the practical political arguments are the important ones now.

The constitutional niceties aside, it is a practical political fact that we elect a president to lead the nation, not only at home but also abroad. Other peoples and governments judge our purpose and resolve by what the president says and does, and their sense of whether he speaks for us all. If his positions are challenged within his own government, if his commitments are repudiated by a majority of Congress, his authority and credibility abroad are fatally weakened. Whatever he says, the world will doubt whether his own nation will back him. Whatever our military or economic strength may be, the world will doubt our capacity to use it.

True, recent history has reinforced our concern that a president can betray his constitutional trust, or make a major error of judgment. That is why our Constitution forbids presidents to legislate, or declare war or make treaties, without the concurrence of Congress. That is why the Constitution also allows the House of Representatives to impeach a president for "high crimes and misdemeanors," and authorizes the Senate to remove him from office. But when Congress delegates less cosmic decision-making powers to the president, especially in the field of foreign policy, it is bad practical politics for Congress to attach a condition that would permit one or both houses of Congress to nullify any particular decision he makes.

We live in an increasingly interdependent, rapidly changing and highly dangerous world. Events abroad can now shock our economy, endanger our security and ignite the nuclear arsenals we have not yet learned to control. Governments fall, alliances shift, opportunities to preserve peace and freedom come up swiftly over one horizon and disappear as swiftly over the other. A great nation must be able to respond quickly and decisively as the world scene changes, by increasing or decreasing its military or economic aid, by changing the disposition of its armed forces, and above all, by making credible commitments to foreign leaders about the assistance it will provide.

But over the past decade, Congress has sought to establish its own veto power over the president's ability to make prompt responses. If new developments make it desirable in the president's judgment to shift military funds to economic aid, Congress has stipulated that he cannot do so unless the appropriations committees of both houses approved. If he deems it in our interest to sell nuclear fuel to India, or to sell military equipment to Israel, Egypt or Saudi Arabia, Congress has barred the sale if a majority of each house objects. And it he decides to move elements of our armed forces into the air, sea or land space of any country, even at its request, or into any situatation "where immiment involvement in hostilities is clearly indicated by the circumstances," Congress has asserted the right to require their withdrawal.

Even if it is constitutional, the congressional veto is a clumsy way to control the president's day-to-day responses to new developments abroad. Congress can only act in public, while a full public presentation of the president's reasons may risk exposing intelligence sources or embarrass those we are trying to support. And congressional reversal of a presidential action is bound to damage our national image, especially in a world where most other heads of government--totalitarian, monarchical or democratic--have the capacity to commit the government they head.

The congressional veto has these adverse effects even if the president's judgment in a particular case appears to the majority of us to be flatly and wholly wrong. But in a close case like the AWACS for Saudi Arabia, the damage we do to ourselves is much worse. We would be proclaiming that the president we elected to lead us and the free world does not have sufficient judgment or power to commit this government to the sale of five aircraft to a friendly nation. If we do not grant him the discretion to make that decision, how can we trust him with the nuclear button, which not even a congressional veto can recall?