here is no doubt that this week's terrorist attacks on New York and Washington were the opening salvos in the first American war of the 21st century. Less clear is just what sort of war this will be and how the United States can ensure that it prevails. George W. Bush, suddenly thrust into the unaccustomed role of commander in chief, faces fateful decisions about the use of American military power in distant, difficult corners of the world. He must design an effective battle plan and couple it with a skillful diplomatic campaign that sustains strong international support.

Some of the initial war talk we have heard from Washington is disconcerting. Paul Wolfowitz, the deputy secretary of defense, spoke of "ending states who sponsor terrorism." That may work as a form of intimidation, but we trust he does not have in mind invading and occupying Iraq, Iran, Syria and Sudan, as well as Afghanistan, nations with a combined population of more than 160 million people.

To be realistic — and successful — in fighting terrorism, the United States will have to rely on intensive diplomatic pressure, severe economic sanctions and united international support to deal with some of the nations that support terrorist activities. Forcing a change of governments in places like Iraq or Syria would require in each case the application of military power on the same scale that was used in the Persian Gulf war, or greater. Changing the behavior of the present governments, however, may be possible through concerted and sustained pressure from the coalition of nations that Mr. Bush is trying to assemble.

For now, at least, the one state where American military power might be effectively used is Afghanistan, where the Taliban-led government is host to Osama bin Laden, the prime suspect in Tuesday's attack. But removing the Taliban from power and hunting down Mr. bin Laden's Afghanistan-based followers would be no easy task, even for America's powerful armed forces.

Trying to dislodge the Taliban, capture Mr. bin Laden and eradicate terrorist training camps from Afghanistan would be extremely difficult if American and NATO forces had to operate from afar, using air bases in Turkey, aircraft carriers in the Indian Ocean and airborne assault troops. Afghanistan, a mountainous land of widely dispersed villages and fiercely independent people, is a general's nightmare and guerrilla commander's fantasy, as the Soviet Union learned after it invaded in 1979.

Even a military campaign launched from nearby nations like Pakistan and the former Soviet republics of Central Asia would be arduous. Ousting the Taliban would probably require a ground invasion leading to the capture and occupation of Kabul, the capital, and other main cities. That would still leave the rugged countryside, where the terrorist base camps are located, beyond American military control. Difficult ground expeditions would have to be launched against the bin Laden organization's scattered hillside encampments.

No warm welcome can be expected from Afghanistan's 26 million people, who have traditionally greeted outside armies with hostility. Controlling Kabul has never given any government or occupier mastery over the rest of Afghanistan. If Mr. Bush wants to wage war there he must understand the risks and plan a campaign crafted to overcome the dangers that American forces would encounter.

The cooperation of Russia, Pakistan and Saudi Arabia, all with airfields and military staging areas within striking distance of Afghanistan, is likely to be critical to success. Some form of Russian support seems possible, and Saudi Arabia is now considering American requests for various kinds of help. Pakistan is more problematic, despite its government's pledges of cooperation. Even if Gen. Pervez Musharraf, the country's military dictator, agrees to support American military action, other army leaders and powerful Islamic fundamentalist groups are closely aligned with the Taliban. Any American victories in Afghanistan would quickly turn into a catastrophic defeat if the war there turned Pakistan, with its 142 million people and nuclear weapons, into an Islamic fundamentalist state.

In the anger and revulsion generated by this week's attacks, it is all too easy to wish for a quick and decisive American military response. But the nature of the enemy, and the sanctuaries where he hides, promise to make this a long and unpredictable war. As it begins, Mr. Bush and the nation must be under no illusions about the battles ahead.