But no green groups or scientific organisations have been invited to the talks. International environmental group Greenpeace has labelled the meeting a "coal pact" dominated by coal exporting and importing nations and producers.

"The meeting's agenda leaves no room for scientific evaluation of the best energy technology policies to reduce greenhouse pollution," Greenpeace clean energy campaigner Catherine Fitzpatrick said on Tuesday.

Green groups said the Sydney climate conference should focus on renewable energy such as solar, wave and wind power and not on existing polluting technologies or technologies that still do not exist except on the drawing board.

Hundreds of green activists are expected to stage protests outside the conference, where business chiefs from firms such as the United States' Rio Tinto, Exxon Mobil Corp and Peabody Energy Corp and Japan's Nippon Steel Corp meet on Wednesday. Energy and environment ministers meet on Thursday.

But the conference is a closed meeting, with host nation Australia not releasing an agenda, and the lack of transparency has raised criticism that little will be achieved.

Australia and the United States say the meeting is a new co-operative between governments and businesses to reduce global pollution through cleaner technology.

Perhaps, but environmental economist Jack Pezzey said the meeting appeared to be a "closed shop" to new energy technology.

"The conference gives every impression of having been put together to favour particular energy and business industries in Australia and America," Pezzey, of the Australian National University in Canberra, told Reuters.

"MISSED OPPORTUNITY"

"A conference like this is a huge missed opportunity for all sorts of interests across conventional fuels, renewable fuels and energy systems, energy conservation, energy efficiency - you name it, it's excluded from this conference."

According to figures released by the partnership, the six nations account for 48 percent of the world's greenhouse gas emissions and 48 percent of the world's energy consumption.

The United States and Australia have refused to sign the Kyoto Protocol, which sets targets for reducing greenhouse gases blamed for global warming, saying it would threaten growth. Developing nations China and India back Kyoto but have nonbinding commitments. However, Japan has binding agreements.

The United States says the new pact will not set fixed greenhouse gas reduction targets, but will compliment Kyoto with practical pollution-cutting measures and will promote economic development.

The Sydney meeting is expected to create a fund to help develop cleaner energy technologies, with Australia reportedly contributing about A$100 million ($75 million).

The gathering was also important for bringing developing nations like China and India into agreements on limiting greenhouse gas emissions, said Professor Anthony Patt, of Boston University's Centre for Energy and Environmental Studies.

But Patt said the Sydney meeting must set binding targets.

"Binding targets signal to industries that they need to implement clean new technologies - like hydrogen, wind, and carbon sequestration - rather than continuing to explore them only as demonstration projects," Patt said in a statement.

"Once industries gain experience using the new technologies, prices will come down, making them competitive with oil and coal."