Global warming is one of this century's great challenges, but nations must be free to choose how they fight it, the United States told a meeting of 16 top economies Thursday.

Billed as a contribution to United Nations talks on climate change, the US-sponsored gathering of major polluters underlined the gap between President George W Bush's call for voluntary measures and binding targets sought by the UN and the European Union.

Bush's initiative brought together senior officials from the richest nations with key emerging economies including Brazil, China and India - the kind of nations the US wants to have covered under any new global pact to curb emissions of greenhouse gases.

Delegates met in Washington as nations gear up for a December conference on the Indonesian island of Bali to launch UN talks on a pact to replace the Kyoto Protocol, whose binding emissions cuts expire in 2012.

"We want this year's UN climate change conference in Indonesia to succeed," US Secretary of State Condoleezza Rice told the meeting.

Washington supports setting an overall, long-term goal for greenhouse gas reductions as a first step, followed by mid-term targets that each government sets on its own.

But UN and EU officials at the meeting made it clear that they expect more than voluntary steps from the United States - which has 5 per cent of the world's population but blasts a quarter of its greenhouse gases into the atmosphere.

Yvo de Boer, the top UN climate change official, praised an EU pledge to lower emissions up to 50 per cent by 2050 compared to 1990 levels.

"We believe that purely voluntary approaches have failed to meet greenhouse-gas reduction goals in the past," said Karsten Sach, an official at Germany's environment ministry.

Rice said efforts to tackle climate change were at a crossroads and laid out the US solution: technology improvements, driven by the private sector.

"Let me stress that this is not a one-size-fits-all effort," she told delegates. "Though united by common goals and collective responsibilities, all nations should tackle climate change in the way they deem best."

Nations risk facing a choice between a clean planet and economic growth, especially in emerging nations where people expect a better life, "from well-paying jobs to automobiles to decent homes," Rice said.

"This current system is no longer sustainable and we must transcend it entirely through a revolution in energy technology," she said.

Rice acknowledged that climate change is a global problem and that the United States is contributing to it as a major emitter, and she pledged US leadership to help reach a new international pact.

She compared the challenge to nuclear weapons proliferation, disease and terrorism.

The two-day meeting in Washington came days after world leaders - and celebrities like former US vice president Al Gore and California Governor Arnold Schwarzenegger - highlighted the challenge of climate change at a United Nations summit.

Bush skipped that meeting, sending Rice instead. But the US administration insists that the Washington talks were meant to complement, not rival, UN negotiations.

Other nations attending were France, Italy, Britain, Japan, Canada, Mexico, Russia, Australia, Indonesia and South Africa.

Outside the meeting, US authorities arrested 47 Greenpeace activists for blocking access to the building after refusing to heed warnings to stop, State Department deputy spokesman Tom Casey said.

Greenpeace said 50 people were taken into custody. dpa tc mm aw