NO nation has ever had the firepower that America now has at its disposal. If any country was ever equipped to wage a successful war on terrorism, assuming this could be achieved by military means alone, then it is the United States.

But, once the initial shock of last week's terrorist atrocity in New York and Washington had subsided, and it was time to turn howls of outrage into plans for retaliation, President George W Bush's instinct has not been to go it alone.

Instead, intense diplomatic activity is now concentrated on putting together an international coalition to support military action. The experience of the Gulf War showed that a carefully-assembled coalition not only provided overwhelming superiority in battle, but also isolated Iraqi leader Saddam Hussein, even among the Arab world, making his defeat inevitable.

Now the US, with Britain at its shoulder, is attempting to build a similar level of support for an attack on the man suspected of masterminding the terrorist strike, Osama bin Laden, inside Afghanistan. Prime Minister Tony Blair has cleared his diary to devote himself to the task, with meetings with German chancellor Gerhard Schroeder and French president Jacques Chirac planned for today, before leaving for Washington to see President Bush tomorrow. "There are a number of reasons why the Americans are keen to secure international support for their action," says Pat Chilton, professor of international relations at Sunderland University. "Militarily, they have a policy of zero casualties, and operations should be planned on that basis.

"It is an extraordinary policy for a country going into a war, but they know public opinion won't sustain casualties. They need allies, therefore, to do the more dangerous parts of the operation, and Europeans have been willing to engage in that in the past.

"But there is another consideration that is just as important: they need allies in order to legitimise the action. Although they have got the force, and they can certainly create a very big band and do a lot of damage, it will very quickly de-legitimise any genuine struggle against terrorism."

But, she argues, President Bush has already sowed the seeds for difficulties in the coalition by his pledge to root out and destroy the terrorists. "He is allowing people to think that they can just go in and get them, and that is very dangerous," she says. "He is going to be caught between what he seems to have promised, that he will be able to go out and eradicate the terrorists, and the need to keep other countries on board with whatever the Americans propose. Once there is military action against civilians, there is going to be a very clear falling off of support.

"Places like Pakistan and Saudi Arabia, where at the moment there is an attempt to maintain good relations and at least gain their approval for military operations, will find it very difficult to support anything other than extremely cautious and carefully-targeted action, the sort that would satisfy public opinion in America."

Pictures of the horrific attack on the World Trade Centre have been seen around the world, provoking widespread condemnation and, in turn, producing a natural coalition in sympathy with the United States. But, even among members of Nato, there may be some reluctance to get involved in a protracted military struggle in the harsh environment of Afghanistan.

"It is going to be very important for Bush to keep the support of the solid Nato members, plus the support of a wider coalition outside Nato," says Prof Chilton. "If Nato support really did start to crack, it would be very difficult for Bush to push ahead with purely unilateral action."

US determination to demonstrate its anger will also create uncomfortable dilemmas for some of its natural allies in the war against terrorism. Russia has had its own problems with terrorists in Chechnya, and the memory of its catastrophic invasion of Afghanistan, but will be unhappy at the prospect of American troops close to its own territory.

"If the Americans play their cards right, they could get an enormously strong coalition, including the Russians and Pakistan, and most of the Middle Eastern countries," says Prof Chilton. "But it would have to be on the basis of a different kind of military operation than the one Bush appears to be promising to the American people.

"The question is, to what extent is that rhetoric, and is he going to allow himself to be talked into a different kind of policy, one with more emphasis on diplomacy? But, the worry is, to what extent does the rhetoric take over, and it becomes very difficult to back down?

"Things are very uncertain at the moment, and a lot will depend on the way this coalition is played out, and whether people can persuade the United States that they will get more satisfactory results doing less damage. If it does start to break apart and the US goes along, they're going to get a lot of flak, not only from the Middle Eastern countries, but also from people who have been working very closely with them."