The Arizona senator was due to propose a cap-and-trade system designed to cut greenhouse gas emissions, in remarks which will clearly separate him from the skepticism on global warming which has marked Bush's presidency.

The initiative will also signal that McCain plans to challenge the Democrats for independent voters in the November presidential election, targetting especially the climate change stance of leading Democratic candidate Barack Obama.

"I will not shirk the mantle of leadership that the United States bears," McCain was due to say in a speech in the western state of Oregon.

"I will not permit eight long years to pass without serious action on serious challenges," he said, in a clear rebuke to the Bush administration.

McCain will also pledge to play a lead role in negotiations for an agreement to come into force after the Kyoto Protocol on emissions cuts, which the United States refused to ratify, expires in 2012.

"I will not accept the same dead-end of failed diplomacy that claimed Kyoto," McCain was to say.

"The United States will lead and will lead with a different approach -- an approach that speaks to the interests and obligations of every nation."

McCain proposed a cap-and-trade system, which sets a limit of total greenhouse gas emissions but allows companies to sell unused greenhouse gas emission credits to other firms which have exceeded their quota.

His plan would seek to return emissions to 2005 levels by 2012, and a return to 1990 levels by 2020. It foresees a reduction of 60 percent below 1990 levels by 2050.

McCain's stance on climate change sets him apart from a large chunk of his party's conservative base, which remains skeptical about the science on climate change.

Bush last month laid out a blueprint to curtail US greenhouse gas emissions from 2025, but critics said it would do little to combat climate change.

The president did not detail any mandates to bring down industrial emissions, and warned Congress against passing new legislation that might "impose tremendous costs on our economy and American families."

Bush also objects to Kyoto because it did not apply binding greenhouse gas targets on fast-growing China and India.

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