"Commercialization of fusion has the potential to dramatically improve America's energy security while significantly reducing air pollution and emissions of greenhouse gases," President George W. Bush said last January, announcing the US change of heart.

The US decision appeared to come at the last minute, as countries that had carried on with the project in the intervening years got ready to put it into effect.

The US Department of Energy, which on December 20 hosts here a final meeting to choose the site of the experimental nuclear reactor, has remained tight-lipped on US participation, declining to comment on the apparent volte-face.

Despite the fact that the ITER project looks so promising, both on technological and economic grounds, so far it has failed to excite much US media interest.

In going back to the project, meanwhile, the United States is looking to take a back seat. It has not got involved in proposing a site for the reactor, although it will contribute around 10 percent of the costs -- around five billion dollars in today's money -- worth 500 million dollars over 10 years.

Washington is also offering to make contributions to ITER in the form of construction work and seeks involvement in the project's administration, as well as scientific research and technological development.

The United States withdrew in 1998 from a project Congress considered unrealistic and costly, but its participation had originally come as pioneer country when the idea was broached by the former Soviet Union in 1985 under the auspices of the International Atomic Energy Agency.

The US withdrawal forced partners Japan, Russia, the European Union and Canada to reconfigure, potentially reducing the budget by half. But five years on after a series of reports were released on the subject, the DoE finally deemed it credible.

"The Bush administration believes that fusion is a key element in US long-term energy plans because fusion offers the potential for plentiful, safe and environmentally benign energy," US Energy Secretary Spencer Abraham announced in January, in explanation of the US return to the table.

"A fusion power plant would produce no greenhouse gas emissions, use abundant and widely distributed sources of fuel, shut down easily, require no fissionable materials, operate in a continuous mode to meet demand, and produce manageable radioactive waste," he said.

The US enthusiasm here to find a way of avoiding greenhouse gas emissions -- blamed for climate change -- comes in contrast to its refusal to ratify the Kyoto Protocol which sought to impose restrictions on greenhouse gas emissions.

The Bush administration had found that protocol too restrictive on US industry.

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