"One cannot expect concrete results," said Gabriel, speaking from the United States.

He said none of the world's top polluting nations would want to show their hands before the UN climate talks in December in Bali, where delegates hope to discuss a successor agreement to the Kyoto Protocol on cutting harmful emissions.

"No one wants to publicly surrender their position because that would damage their negotiating position," said Gabriel, who will attend the Washington meeting.

"Obviously, there is the concern -- that is not without justification -- that the conference could be used to undermine the conference in Bali," Gabriel said.

"But that is getting harder because the climate protection movement in the United States is gaining momentum," he said.

As the world's leading emitter of greenhouse gases, the United States has said it wants to take a leading role in combating climate change.

But critics from the US environmental movement and elsewhere say its resistance to binding targets on reducing emissions makes coordinated international progress on the issue difficult.

Ahead of the Bali conference, Bush had called the meeting of major emitting countries in Washington for Sept. 27-28 to work out future cuts. It remains unclear how the meeting will fit into the broader UN efforts.