IN AUGUST of last year, President Bush began talking about his nebulous "New World Order."

In his State of the Union address last week, Bush spoke of the upcoming "American century."

Well, what's it going to be? A "New World Order" based on collective security would be a welcome improvement in the international political arena. An "American century" aspiring to U.S. international hegemony is a bogus, quixotic dream.

BUSH'S RECENT HINT of a new Pax Americana that would begin after Saddam Hussein's defeat raises unsettling images of John Winthrop's ideal of America as a "city on a hill," John Foster Dulles's notion of America as savior or even the 19th century vision of America's "manifest destiny."

But since the 1970s, international relations experts have thoroughly documented America's economic decline. Relative productivity and the American share of world trade have dropped; even optimists such as Joseph S. Nye recognize that American hegemony has ended.

The last time the U.S. tried "to preserve our national honor as guarantor" was during the Vietnam War. This objective, according to a memo from Assistant Secretary of Defense John McNaughton to Lyndon B. Johnson, was the prime motive of U.S. intervention in southeast Asia. He thought a pullout would irreparably damage U.S. credibility throughout the world. So the U.S. remained in Vietnam. Ultimately, U.S. credibility was damaged precisely because it chose to do so.

By the late 1960s, even European allies had denounced U.S. involvement in Vietnam. The negative consequences for America's reputation in the Third World still persist today.

INSTEAD OF FOCUSING on post-war American hegemony, Bush should concentrate on achieving collective security through a strong United Nations. With the end of the Cold War, this goal is possible. Yes, the U.N. was viewed as a joke in the context of a bipolar Cold War world; but its capacity for effectiveness has been demonstrated in the Gulf conflict. Bush should never lost sight of collective security--while fighting the war or while waging the peace.

The remarkable international coalition formed to oppose Saddam Hussein would seem to bode well for the future of collective security. But Bush's hasty move to end economic sanctions clouds that future considerably.

The very existence of the war will make future attempts at coalition building--both internationally and at home--very difficult. Last month, Professor Stanley Hoffman wrote in The New York Review of Books that the U.S. should not go to war in the Gulf because the stakes for collective security would be too high.

Hoffmann maintained that if the anti-Iraq coalition failed to defeat Saddam Hussein cleanly and quickly, the U.S. could retreat into isolationism and destroy the possibility of collective security to halt future Saddamism. "Only a miraculously successful war--a swift victory through a limited resort to force--would dispel these dangers," Hoffmann wrote.

Despite the favorable course of war thus far, the well-entrenched Iraqi troops will not leave Kuwait without a bloody ground war. As Hoffmann put it, a large American body count "almost ensures that the U.S. will not again provide the leadership--not to be confused with preponderance--required to make [collective security] work."

In addition, a bloody and internationally divisive quagmire could totally preclude the possibility of future alliances, no matter how much domestic support exists. The coalition could easily disintegrate over how long to stay in Iraq or the cost of the operation. By embroiling the U.S. in a premature war, Bush has put collective security on a tightrope.

Recent signals from the State Department are not helping. After months of tough rhetoric calling for the removal of Saddam Hussein, Secretary of State James Baker said last week that the president would be willing to half hostilities if Saddam made "an unequivocal commitment to withdraw from Kuwait." Bush should insist that Saddam actually pull out of Kuwait completely before stopping the war effort. The U.S. should stick to the agreed-upon goals around which the coalition was formed.

The U.S. should also continue to praise Israel for its restraint. Although most of the Arab allies have assured other coalition members that they will remain united against Saddam Hussein, an Arab-Israeli war could only hurt the chances for more Western-Arab cooperation, which will be essential if collective security is to work.

BECAUSE OF economic realities, the days when the U.S. can act unilaterally are over. In fact, as Hoffmann put it, "no single nation will be capable of playing world policeman" in the '90s. Still, there must be a united force (most logically, of course, the U.N.) which can effectively stop future Saddams. And this force must be prepared to negotiate workable solutions for cases less clear-cut than Iraq's invasion. Most important, this force must be prepared to enforce those solutions.

It may turn out that this war will make collective security impossible. But President Bush and the other coalition leaders should kick and scream before they allow it to wither. Not for the sake of the U.S., but for the sake of the world.