Suddenly it's all the rage to pound on the doors of the Reagan administration, demanding a foreign policy. A "major foreign-policy speech" would help, or even, God save us, a Reagan Doctrine.

Then, the critics cry, we would have an honest-to-goodness Great Debate on foreign policy. In the end, everybody at home and abroad would know what to expect of the United States -- and what the United States expects of the rest of the world.

It is a truly beautiful thought, powerfully appealing to orderly minds. Look here, say those who yearn for coherency, at what Secretary of State Haig said on his China trip, and at what the president said in his press conference, and at what Defense Secretary Caspar Weinberger said on a talk show and at what White House counselor Ed Meese said, trying to tidy up. It simply doesn't hang together.

That's right, it doesn't. But the reasons why it doesn't hang together are precisely the reasons why a speech cannot a foreign policy make. It works the other way around.

True, a White House call on the principal foreign affairs advisers for presidential speech material does concentrate the mind; it can have a therapeutic effect on internal conflicts. The final product may even get all the top people saying the same things -- for a time.

But a speech (and still less a doctrine) is no substitute for a decision-making procedure that brings the free-wheelers and the power-strugglers forcefully into line with the president's purposes. Once that's done, a "foreign policy" will emerge by a sort of extrusion process, in which the hot metal of competing plans and proposals is forced by political, bureaucratic and -- above all -- presidential pressure through the die of crises and conditions around the world.

The merging shapes and patterns may someday deserve to be enshrined as doctrine.

But from all the available evidence, the Reagan administration is a long way from being ready for that day. This may strike many of the president's critics as very near dereliction of duty. But no matter: history -- Ronald Reagan's and that of his predecessors -- argues for understanding and patience all around.

Remember the pulse-racing Kennedy Inaugral Address ("We will pay any price, bear any burden, meet any hardship, support any friend, oppose any foe . . .")? It took the Bay of Pigs, the Cuban Missile Crisis and countless other encounters with the real world to produce Kennedy's truly memorable American University speech, laying out a balanced and measured foreign-policy approach two years later, in June 1963.

Only a handful of brave senators questioned Lyndon Johnson's Tonkin Gulf Resolution -- a pronouncement of high policy that became the basis for the massive escalation of the American effort in Vietnam. Jimmy Carter spent a full term trying to explain what he really meant in his maiden foreign-policy speech at Notre Dame early in his first year. His second effort at Annapolis, in mid-term, was denounced as a transparent papering-over of irreconcilable differences between his national security adviser and his secretary of state. In the current issue of foreign policy, former undersecretary of state David Newsom castigates the Carter Doctrine's threat of "military force" if necessary to protect the Persian Gulf as a policy growing out of "last minute pressures for a presidential speech." He holds up the Eisenhower Doctrine, adopted by congressional resolution, as a model of how to proceed.

But that, too, was a rush job with sweeping implications: "Overt armed aggression (in the Middle East) from any nation controlled by international communism" would be resisted by "the armed forces of the United States." If Congress was consulted in advance, the likeliest beneficiaries in the area were not. As with the Carter Doctrine, there was no real military force to back it up. Only by playing fast and loose with the facts did its ultimate invocation in Lebanon fit its terms.

The Nixon Doctrine, spelled out by its author at an unrehearsed background press conference at the end of a long day on the island of Guam, had a short shelf life. And Nixon, by that time, had just one real foreign policy adviser, Henry Kissinger, in whom he reposed much trust.

Reagan has a cast of, well, three or four, of distinctively different persuasions. He has, in addition, his own instincts and predilections on Taiwan, Arab "refugees," the international communist conspiracy and the power of pure patriotism to muster, without a draft, all the manpower his defense buildup will demand. They do not add up to a foreign policy fit for current consumption -- or events.

Soon enough, the president will have to bend his principal aides to his purposes -- or replace them. But first he's going to have to settle on his purposes. Given where he's starting from, I hope he has as many firsthand encounters with foreign dignitaries as he can fit in, and goes right on dispatching envoys around the world. Events permitting, I hope he takes his time.