Just as US diplomats must constantly face down claims that they have retreated from the region, particularly Southeast Asia, to concentrate on other demands, they must deal with a fast-changing world.

China, of course, has grown in stature and strength, and displayed considerable diplomatic nuance over the past decade, forging new ties with nations across the region; North Korea is now nuclear armed, while a long-dormant Russia, flush with oil revenues, has embarked on a regional charm offensive.

A war-torn and battle-scarred Uncle Sam is now struggling to assert the primacy he once took for granted.

Part of it is a game of perceptions. It is a fact that the US remains the dominant military power in the region and will remain so for decades, despite China's military build-up.

Washington has also forged a deeper and broader engagement with Beijing, reflecting increasingly complex economic and diplomatic interests. It also maintains alliances and friendships with traditional allies such as Japan, South Korea, Thailand, the Philippines and Singapore.

Yet there is a nagging sense in the state rooms and diplomatic salons of the region that Iraq has obsessed the US to a dangerous extent, forcing it to drag its gaze away from the region at crucial times.

'There is an alarming perception out there that Washington is just no longer engaged with the region in the way it was,' one Southeast Asian diplomat said.

'They've got too much on their plate and they have done a poor job of juggling priorities. They've turned away just as China and even Russia have been seeking to make up for lost ground.'

The Association of Southeast Asian Nations has appeared particularly rattled at times, with US Secretary of State Condoleezza Rice conspicuous by her absence at meetings over the past three years as events elsewhere drag her away.

A long-planned gathering of the leaders of the 10 nations and US President George W. Bush to mark Asean's 30 years never quite happened - in part because of the diplomatic difficulties of dealing with Asean bad boy Myanmar.

And it is not just piqued Southeast Asian officials muttering under their breath about US commitments. The question of America's place in the world is troubling some of the finest minds in Washington as the controversial Bush administration enters its twilight months.

A number of surveys suggest ordinary Americans are deeply concerned at Washington's competitiveness on the global stage amid Iraq and a tumbling dollar. They are also concerned at its international standing after the discovery of torture by US troops at Abu Ghraib prison and the lack of legal transparency surrounding Guantanamo Bay.

Andrew Kohut, president of the Pew Research Centre, recently told a Washington seminar that Pew's international surveys noted a growing discomfort and suspicion of America's unrivalled power, even among traditional allies. Some wished there was a rival as powerful as the US. 'Shocking answer,' Mr Kohut said during a talk last week on America's place in the world at the Centre for Strategic and International Studies.

'The only good thing ... is all of the nominees, particularly China, are rejected by even huger majorities than the percentage of people who say they are uncomfortable with our power.'

William Cohen, a former Republican senator and defence secretary under president Bill Clinton, told the gathering the US had to work harder to strengthen ties with friendly democracies such as Australia, Japan and India, even as it forged a deeper relationship with China.

These allies must be encouraged to work with the US to ensure China developed peacefully.

'China's going to continue to grow in its power ... and we have to take every action we can to ensure as best we can that that power is integrated in the international community in a peaceful way,' he said.

The US presidential candidates have all stressed the need to re-energise America's regional diplomacy, particularly Republican nominee Senator John McCain and Democratic hopeful Senator Barack Obama. Both are particularly keen to shore up traditional relationships with the likes of Japan, South Korea and Thailand.

The US' troubles in the past five years do not mean that it is all going to run China's way in terms of regional diplomacy in the near future.

Just as US leaders want to better engage the region, many governments in the region want a stronger and more engaged US presence, even as they court China, Russia or India.

Former enemy Vietnam, for example, is one nation eager to forge a deeper friendship, in part as a strategic counterweight to its northern neighbour.

'On balance, we want the US back and fully engaged,' said the Asean envoy - remarks echoed in Singapore, Seoul and Tokyo.

'Washington can be hard to live with, but we sure as hell don't want to live without them.'