"I think the announcement by President Bush last week was significant and important, and it is absurd to say otherwise, since it moved things on," said Blair, who stands down as premier in three weeks' time, referring to a speech by Bush about establishing a US-led initiative to tackle global warming.

"The key elements of this (deal) are an acceptance that the climate is changing in a dangerous way as a result of human activity.

"Secondly, we need a global agreement that includes all the main players, including China and America, and at the heart of that there has to be a global target for a substantial cut in emissions. I believe it is possible to get all that way."

Blair said his best case scenario for the summit would be a final communique containing a commitment to cut carbon emissions by 50 percent of 1990 levels by 2050.

However, he said if that was not possible, then there needed at least to be a framework agreed for a deal down the line.

"You could have a situation where this is agreed at the G8 -- which is my preference -- or you could see how it is agreed in principle, but you have to work out the details later.

"The important thing is that if we get an agreement to the idea of a global target of a substantial reduction in emissions, and it needs to be clear that is in the order of 50 percent. You are not talking about 20 percent.

"I will be going for the maximum and I will want more."

The United States has shown little inclination to join major European powers in pushing for UN-backed restrictions on greenhouse gas emissions, with Bush last week putting forward new proposals of his own that appeared in contradiction.

One key concern for the United States is that, unless China and India, two of the world's most-rapidly industrialising nations, are on board with any deal, it does not serve other parties' interests -- including the United States -- to sign.

Blair told the Guardian that while he was not totally clear on what Bush would agree to over three days of talks at the summit, he was sure that Bush's recently announced initiative was not a ploy to undermine the United Nations or the G8.