"The trouble with the future," French essayist Paul Valery sagaciously observed, "is that it is not what it used to be" -- a sobering thought that, and one that commends itself to all Ronald Reagan's foreign policy advisers and to reagan himself. In pursuit of a peaceful and prosperous future, Reagan's most important cabinet appointment -- if he ever makes one -- will be his secretary of state. An American president can indulge the pols' traditional lust for tomfoolery in almost any other area and all it costs his loyal subjects is money, convenience and liberty. In the area of foreign policy, it costs lives, nowadays millions of lives.

At the State Department, America must have a man who commands respect in Europe, Moscow and Peking. The next secretary of state will be presiding over a department demoralized in some areas and trivialized in others. He will have to be able to administer and revise it. During the next four years, the American military will, for the first time in the postwar period, be inferior to that of the Soviet Union. The next secretary of state must, therefore, understand diplomacy, strategy and military balance. Finally, he will have to understand the tensions and communications channels that exist between the White House and Congress.

Who is the man for this job? Alas, George C. Marshall is dead. John Quincy Adams is in the same unfortunate condition. In American today, the pickings are slim. Yet I have a recommendation. I recommend Alexander Haig.

In Europe, Haig is respected at every governmental level. Moreover, as former supreme commander of NATO, he is esteemed by large numbers of ordinary citizens. He himself has a deep knowledge and understanding of the Soviet Union, the Middle East, China and Europe. There is none of the sophomoric dreaminess in him that characterizes Jimmy Carter's foreign policy geniuses, and when in Poland he would bring along a proper translator.

Haig knows the military. He understands geo-politics and has a solid grasp on dimpomacy. That he was an understudy with Nixon and Kissinger only increases his heft in foreign policy circles abroad. In the 1960s, he made his way up through the Pentagon bureaucracy and the National Security Council, providing his understanding of bureaucratic ways. During his last years in Washington, he worked both in the executive branch and with Congress. In an era when Congress has arrogated a large role in foreign policy-making, such firsthand knowledge of the honorable representatives' touchy ways is invaluable. Finally, Haig has carried himself through a long public life with dignity, displaying strength and flexibility that does no violence to principle.

The inhabitants of the world's foreign ministries have become increasingly alarmed by America's eccentric performance on the world stage. They are coming to see us as a nation abounding in bizarre enthusiasts. Haig is the only candidate for State who might instantly set our allies' apprehensions to rest without creating an enormous furor at home.

The only other candidate for State possessed of this urgent attribute is, of course, Henry Kissinger. Yet somehow Henry, the fabled charmer of all Georgetown, has managed the amazing feat of becoming persona non grata to half the liberals of the republic and to half the conservatives. Were he to be returned to his old chair in the State Department, conservatives and liberals might promptly begin killing each other.

And so, ladies and gentlemen, I give you Secretary of State Alexander Haig. Every columnist should make it a practice to say something constructive at least once a year; here is my stab at it. The case for Haig strikes me as intelligent and compelling; I therefore do not wince at making it.

Naturally, given the novel standards of American politics, my case would be strengthened if I could report that Haig is a woman, for it seems to be a desideratum of the utmost urgency with many pundits that Reagan choose his cabinet on the basis of sex. Alas, all available evidence suggests that Haig is a male, nothing more. This shortcoming can only be overcome with the greatest difficulty and, if it were, I am not sure the foreign diplomats would understand.

For a change, the American pundits are going to have to take the world as it is. Haig would bring dignity, prudence and professionalsim to the conduct of American foreign policy. That is, at this point in our history, quite enough.