It has seen off the Soviet Union and helped restore peace in the Balkans, but is now facing its most serious challenge yet.

Nick Morrison looks at where it's all going wrong for Nato.

SPRINGING out of the rubble of post-war Europe, it has been the cornerstone of our defence policy for more than 50 years. Founded on the twin pillars of knitting together the security of the United States and western Europe, and of providing a bulwark against the challenge of the Warsaw Pact, Nato has played a pivotal role in ensuring we can rest easier in our beds.

But now the North Atlantic Treaty Organisation is in danger of splintering back into the chaos from which it emerged. The refusal of France and Germany to sanction supplying Turkey with defensive equipment has revealed the extent of the gulf between the United States and Britain on the one hand, and what US Defence Secretary Donald Rumsfield dismissively calls "old Europe" on the other.

With the US apparently determined to oust Saddam Hussein, and with France and Germany remaining deeply sceptical about military action, a natural suspicion has hardened into open hostility, with neither side prepared to spare the other's blushes.

And the dispute has potentially wide-ranging consequences for the future of Nato itself, according to David George, politics lecturer at Newcastle University.

"This is a very, very serious blow to Nato. It will weaken Nato, and in the long run it could bring its whole future into question," he says.

The dispute centres on a proposal to supply Patriot missiles, anti-chemical and biological weapons units and early warning systems to Turkey, the only Nato member to border Iraq, after Turkey invoked the North Atlantic Treaty, under which a Nato member can require other members to come to its aid if its territory is threatened.

France and Germany, along with the unlikely rebel of Belgium, blocked the move, arguing that it would make war more likely when there was still a chance it could be avoided, and instead called for more weapons inspectors to be sent to Iraq, along with UN troops.

But this seems to be an abrogation of their treaty responsibilities, according to Mr George. "I think it is just posturing, and asinine posturing at that," he says. "If the treaty means anything at all, the key to it is that if one member is threatened with an attack, the other members come to its aid. To try to prevent that is totally contrary to the entire essence of what the treaty is about."

With the transatlantic alliance now looking shaky, one consequence is to put the future of Nato itself into doubt, Mr George says.

"A lot of people raise the question, after the Cold War, of what exactly is the point of Nato, since the whole thing was designed to deal with the Soviet Union and its Warsaw Pact allies and the threat they posed of nuclear and conventional war," he adds.

"With all of that having disappeared, the question is what future Nato has. The short answer is that to date it has been clearing up the mess in its backyard, in humanitarian intervention in Bosnia and Kosovo. But if a member state is attacked or threatened and the other states are not willing to allow defensive arrangements, then you might as well kiss Nato goodbye."

Behind these manoeuverings is the long-mooted proposal to create some kind of European rapid reaction force, as an alternative to Nato. France, in particular, has had a semi-detached relationship with the alliance in the 54 years since its creation, and both Paris and Berlin would welcome a body which had a less US-dominated voice.

But Mr George says the Franco-German reluctance to get involved is unlikely to slow US preparations for war, and instead may bolster the hard-liners in the White House.

"The hawks in the administration will be saying 'I told you so', and I think it will make them less inclined to wait for a second UN resolution. They might just decide it is not worth wasting any more time and effort on this.

"It might well be that the long-term thinking is that Europe can be a counterweight to the US, but I think this would be very foolish, because it is the US which has all the hi-tech military equipment."

But, serious as this latest development undoubtedly is, he says it is unlikely to lead to the break-up of Nato, at least in the short-term.

"Nato is not in its death throes. This is a heavy blow, no doubt about it, but it is only when tempers have cooled that people will be able to sit down and sort out what Nato is for," he says.

Pat Chilton, professor of international relations at Sunderland University, agrees that it is too early to write Nato off, but says this latest spat is a serious challenge.

"I don't think it means Nato is doomed, but what may happen is that the Americans will turn more towards their ad hoc alliances, which is what has happened since the end of the Cold War, and Europeans will turn to acting independently of the Americans," she says.

"Nato is not something anyone is going to give up in a hurry, but it is going to be seriously weakened and it may end up being sidelined."

But Prof Chilton says that, far from this fall-out being the result of France and Germany welching on their treaty obligations, it instead flows from their determination to avoid war if at all possible, with the belief that a military build-up in Turkey makes conflict more likely.

And she says the trigger for the split comes from Tony Blair organising a show of solidarity from eight European countries, including Spain and Italy, in support of the US stance last week.

"Neither France nor Germany have said they would not defend Turkey, but they have refused to set up the Nato collaboration in the formal way that Rumsfield required," she says.

But with Rumsfield talking about going outside Nato if necessary, the writing may be on the wall for the organisation's future as a serious player in resolving international disputes.

"There is an unease in various parts of Europe at being automatically tied to American foreign policy. Nato is supposed to be a democratic institution, but everybody knows that the US is the biggest player," says Prof Chilton.

"There is still a use for Nato if it is recognised by the United States that there has to be a reasonable balance between leadership and democracy. But if that goes out the window, as Rumsfield is prepared to do, that will be a very bad day for Europe and the transatlantic alliance."