It won the cold war, but now Nato has to finally face up to another fearsome enemy � change. By Diplomatic Editor Trevor Royle

NATO is in danger of getting itself broken beyond repair so let's fix it before it's too late. That is the stark message facing the alliance's diplomats and military commanders at the end of one of the edgiest weeks they have ever faced.

The main problem is to be found in Afghanistan, where the alliance has had its first prolonged taste of real combat in command of the International Security Assistance Force (Isaf). More than 42,000 troops are under its command, coming from 39 countries including the full complement of 26 Nato members. However, its future is now in doubt following a Canadian threat to withdraw 2500 combat troops from Kandahar.

On the one hand, the US and its main ally, Britain, want Nato's European members to make a greater military contribution to the war effort to offset the Canadian threat. On the other hand, most of the European governments in Nato believe that the impasse in Afghanistan is more likely to be solved by the imposition of law and order and the subsequent implementation of education, economic aid and a modern infrastructure.

The consequences of that disagreement over policy and its effects on the future of the 59-year-old alliance were put into context by a senior British Army officer when he said: "Nato held its own against Soviet military power throughout the years of the cold war. Now it's in danger of being brought to its knees by a handful of hawk-faced men armed only with Kalashnikovs, RPGs and an overwhelming sense of their own worth."

Like so many problems to have surfaced in the aftermath of the cold war, when Nato had to reinvent itself to confront the realities of a post-communist world, this latest problem has been festering for some years. When Nato came into being on April 4, 1949, as the North Atlantic Treaty Organisation, the certainties were obvious: the West was threatened by the Soviet Union and its Warsaw Pact allies, and the new alliance guaranteed continuing US superpower commitment to the defence of western Europe.

The philosophy was relatively simple. Members retained national command of their forces in peacetime, but in time of crisis they contributed to collective security through Nato's Supreme Headquarters Allied Powers Europe (Shape) based in Belgium. In deference to US military superiority, especially its huge nuclear arsenal, Shape was always commanded by a US four-star general. In 1952, Greece and Turkey were admitted to Nato to help guard the southern flank. Three years later, the alliance expanded further by allowing West Germany to become a member.

Like the later enlargement which followed the end of the cold war and brought the membership to its present level of 26 countries, this process of expansion caused a good deal of turmoil, especially among the European members who had to balance the requirement for collective security with their own need for retaining democratic integrity.

President John F Kennedy made the most pertinent remark about the alliance in 1962, when he said of it: "I want two strong towers in Nato, one American and one European." This was balanced by the more realistic comment from Lord Ismay, a British secretary-general of the alliance, who commented five years before that Nato had come into being "to keep the Russians out, the Americans in and the Germans down". Against that historical background, the alliance has been struggling to find a new role in the post-cold war world. It intervened effectively in Kosovo in 1999 to protect the Albanian majority and to bring about the demise of Serbian President Milosevic, but that effort had to be put in a fresh perspective with the advent of the war against global terrorism in 2001. At the time of the terrorist attacks, Nato pledged full support, citing article five, which states that an attack on one member is considered an attack on all members, but far from instilling confidence in Washington, this well-meant move was politely put to one side, with the Bush administration arguing that it would adopt an "a la carte approach" to facing up to those responsible for the attacks.

Thus was born the US unilateralist approach that led first to the attacks on Afghanistan to unseat the Taliban government in 2001 and then to the regime-change operations in Iraq two years later. During that time the relationships within the alliance became ever more peevish, and there was a serious split between Washington and most of the European capitals, especially Paris and Berlin. From the outset it was clear that the US policy could only prosper because Russia was weak, but seven years later things have changed. Russia is on the way back to becoming a global power and President Vladimir Putin quickly took advantage of the disarray in Nato ranks to hint that there could be a new arms race.

Last week, the problem finally exploded with a two-barrelled blast at the alliance from Washington. First, defence secretary Robert Gates told the US Senate's armed forces committee that Nato was in danger of becoming a "two-tiered alliance" after Germany turned down his demand for more combat troops in Afghanistan. Then, during a lightning visit to Kandahar with Britain's foreign secretary David Miliband, secretary of state Condoleezza Rice kept up the pressure on the reluctant members of the alliance.

"Frankly, I hope there will be more troop contributions and there needs to be more Afghan forces," she told reporters during the flight from London where she had begun her visit. She then went on to say that Nato members must "give enough military power to do what needs to be done on the front end of the counter-insurgency effort".

Rice's intervention was made more telling by the fact that she and Miliband were heading towards Kandahar, one of Afghanistan's hot spots where the recalcitrant Nato countries in question refuse to allow their forces to serve. The coincidence was not lost on Nato defence ministers meeting at the same time in the Lithuanian capital of Vilnius, where Nato secretary-general Jaap de Hoop Scheffer rejected allegations that the alliance was in danger of splitting and claimed that Nato represented "one alliance". However, as was widely anticipated, the meeting yielded no fresh offers of troops, and the alliance remains as divided on the issue as ever before.

"I don't think that there's a crisis, that there's a risk of failure," Robert Gates told the meeting. "My view is that it represents, potentially, the opportunity to make further progress faster in Afghanistan if we had more forces there."

In response, new member Poland offered an additional 1000 troops, and France is considering the deployment of a battalion of airborne forces to reinforce the Canadians. The Germans, however, remained obdurate that they would neither increase the size of their deployment, nor would they change the rules of engagement which prevent their soldiers taking part in combat operations.

"I think we are doing our part fully in Afghanistan," claimed their defence minister Franz Josef Jung, who also pointed out that his country's 3200-strong contingent was the third largest in Isaf.

The heart of the quarrel remains troop levels, but there is another problem beneath all the posturing about who does the most to make Nato more effective in Afghanistan. In the months ahead, once the weather gets warmer, the Taliban will be reopening their military campaign, and Nato commanders know that it promises to be what one senior British officer called "a massive punch-up".

For Nato it will be a testing moment and one that will be the measure of the military deployment, but some seasoned veterans with long experience of Afghanistan, including Rory Stewart, a former diplomat and Black Watch officer, have already questioned whether more firepower is the answer. "I think we have to be very careful, above all, of appearing to be engaged in colonial politics," Stewart argued in a television interview last week. "I think Afghans are justifiably very suspicious of foreigners coming into their country, particularly with over 40,000 soldiers. People should stop talking about creating a gender-sensitive, multi-ethnic centralised state based on democracy, human rights and the rule of law."

The problem is that Nato is not geared up to that kind of thinking, even though it is beginning to concentrate on training the Afghans to take over responsibility for their own security. The alliance was formed to defend the West against attack from the Soviet Union. During that time it never fired a shot in anger, and now it has been tasked to fight what many believe is the wrong war in the wrong place at the wrong time.

"Afghanistan is still considered by the security community as the make-or-break mission for Nato, and the urgency of the situation cannot be overstated," argues Kate Clouston, an associate of the Royal United Services Institute, in a paper on the alliance's operations in Afghanistan for the independent think tank. "Substantial reform by Nato allies is needed now if the alliance is ever going to be ready to hand over control of the currently unsecured provinces to Afghan national forces."