As the shock of September 11 wanes, attention is increasingly focused on the anticipated U.S. military response.

The United States must find out who was responsible for the attacks, determine what is required to eliminate the threat, and conceive a strategy to meet that challenge. America’s allies-from Europe to East Asia to the Persian Gulf-are potentially an important part of that strategy.

In the immediate aftermath of the hijackings, friends and foes alike pledged support for any U.S. response to the terror. Within days, though, second thoughts surfaced.

To the extent that U.S. allies’ hesitation arises from concern that Washington may be tempted to indulge in hot-headed revenge, that hesitation is justifiable. The United States has a responsibility to craft an appropriate military response, balancing the security imperative to wipe out those responsible for the September 11 events with a healthy appreciation for the unintended consequences of U.S. military activities.

But U.S. allies bear a tremendous responsibility as well.

The NATO countries, Japan, and South Korea have enjoyed mutual defense pacts with the United States that have amounted to a multi-billion dollar U.S. taxpayer-financed defense subsidy for more than 50 years, along with the assurance that the U.S. military would stand by them through any threat.

Now it’s time for those allies to demonstrate support for the United States through more than words. The responsibility of those countries, some of which may owe their very existence to the United States, is no less than to support any reasonable request Washington might have as the United States faces an unprecedented threat to its homeland.

A reasonable request would be any request that a) is part of a well-conceived strategy that meets defined security objectives; b) seeks political, economic, or military support that an ally is in a position to offer; and c) will not create a domestic backlash that poses a threat to the country’s political and economic system.

Such a request may demand sacrifice, even hardship, on the part of U.S. allies-just as U.S. support for these countries has required the sacrifice of American blood and treasure for decades. Unfettered access to air space and military bases, logistical support, diplomatic support, intelligence sharing, law enforcement cooperation, economic contributions and, perhaps, the contribution of military personnel would be reasonable requests.

Saudi Arabia, Kuwait, and the other U.S. allies in the Persian Gulf region also have an obligation to support the United States right now.

As in the case of some other allies, many of the regimes that rule these states also owe their existence to the United States. That is true of Kuwait and Saudi Arabia in particular, which relied on the United States as their national security 911 when Saddam Hussein took over Kuwait in 1990. Moreover, assuming that Saudi-born multimillionaire Osama bin Laden is indeed behind the September 11 incidents, it was Washington’s support of the Persian Gulf countries that is likely the chief reason the United States came under attack this month.

This translates into a hefty obligation on the part of Persian Gulf region allies. Full access to intelligence and complete law enforcement cooperation, which often have not been forthcoming in the past, are critical-after all, bin Laden hails from Saudi Arabia and there are many in that country who support him, financially and otherwise.

Washington may also justifiably request economic support. In light of the U.S. taxpayer investment in the defense of the southern gulf states since 1991, cash contributions would not be unreasonable. America’s Persian Gulf allies should also pledge to keep oil production at its current levels.

Washington may also seek political support, particularly insofar as it can help prevent a sense among Muslims that the American response to terror represents a clash of civilizations.

In deference to the domestic challenges that these Persian Gulf countries face, it’s probably best that Washington not ask for direct military support, which would likely be of little practical use in any event.

And what happens if America’s allies-whether in Europe, East Asia or the Persian Gulf-fail to come to the aid of the United States?

The United States should simply withdraw from NATO if the alliance withholds support, or remove U.S. troops from recalcitrant countries in East Asia or the Middle East. That should happen immediately because the United States faces its own national security threat and cannot afford to waste a single soldier, aircraft or ship on fair-weather allies.