BRUSSELS - Expect triumphant rhetoric this week as NATO expands deep behind the former Iron Curtain.

And scant mention of the fact that the seven new allies from eastern Europe are joining an organization mired in self-doubt, as the range of new enemies and challenges make its rationale of military action by consensus look increasingly outmoded.

US Ambassador to NATO Nicholas Burns, briefing reporters ahead of the accession ceremony in Washington, hailed the enlargement as "perhaps one of the most significant moments" in the 55-year history of the trans-Atlantic alliance.

"There is now an opportunity to think of Europe as one continent that is whole, that is...democratic and free and that is living in peace for the first time in hundreds of years."

The entry of Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia and Slovenia into an alliance forged to fight the Cold War is unquestionably a remarkable turn in history: 40 per cent of NATO's 26 members will now be former communist states.

It will shift the US-dominated alliance's centre of gravity eastwards, bringing it nearer to the Balkans, the south Caucasus, the Middle East and Central Asia, all potential breeding grounds for NATO's post-September 11 enemies: terrorism and the spread of weapons of mass destruction.

Yet for all that, analysts say NATO is in deep trouble.

"The paradox is that, just as central and eastern Europeans arrive at their destination in the west, the Western alliance they have worked so hard to join increasingly appears in disarray," wrote Marshall Fund fellow Ronald Asmus in the alliance's in-house magazine, NATO Review.

To be fair, Asmus, a German, was writing just a few months after last year's bust-up at NATO over the US-led invasion of Iraq.

Since then, tempers have cooled. NATO has taken command of the multinational peacekeeping mission in Afghanistan - its first operation outside Europe or North America - and is now considering a role in post-war Iraq.

Sharp decline

But Sean Kay of Ohio Wesleyan University says NATO has not adapted sufficiently to new security threats since the loss of its defining enemy, the Soviet Union, and that some of its members are losing faith in it as a useful institution.

"The only countries that seem especially enthusiastic about NATO right now are the new members. That will likely wane when they begin to realize that their quest for membership has ended up with their joining an institution in sharp decline," he said.

He said the best illustration of this was the virtual absence of serious debate on enlargement in the US Senate - despite concern about "free riders" joining an alliance already struggling to improve its military capabilities.

To transform itself for security crises of the 21st century, NATO is creating a rapid response force to fight wars.

However, the rule of decision-making by consensus may hamper the timely deployment of this force, because a rejection by even one ally would keep it in the barracks. Last year's month-long tussle over whether to bolster Turkey's defences ahead of the Iraq war is an example of how action can be blocked by a few.

In any case, many doubt that Washington - even though it came up with the idea for a NATO Response Force - would want to subject its war fighting strategy to the consensus process.

Kay said NATO has worked best as a peace support force, particularly in the western Balkans over the past 10 years, but that even here it may be reaching the limits of what it can do.

"The more fundamental problems in Iraq and Afghanistan, and still in Kosovo and Bosnia...are civilian," he said. "The high demand is going to be for multinational police forces, infrastructure rebuilding and economic engagement. NATO offers none of these capabilities directly; the European Union does." (Agencies via Xinhua)