President Obama will announce tough new nationwide rules for automobile emissions and mileage standards on Tuesday, embracing standards that California has sought to enact for years over the objections of the auto industry and the Bush administration.

With a series of compromises on the stickiest issues behind them, the House Energy and Commerce Committee is poised to approve far-reaching legislation on energy and global warming by the end of next week. Where it goes from there remains highly uncertain.

An internal government memorandum that came to light on Tuesday challenged the scientific and economic basis of a proposed Environmental Protection Agency finding that climate-altering gases are a threat to human health and welfare.

After eight years largely on the sidelines of the international policy debate on climate change, the United States is prepared to lead negotiations toward a new global warming treaty, Secretary of State Hillary Rodham Clinton said Monday.

Secretary of State Hillary Rodham Clinton addressed delegates at a climate and energy conference on Monday in Washington.

Obama administration officials said Wednesday that an ambitious energy and climate-change proposal sponsored by House Democrats could help create jobs and reduce greenhouse gas emissions, but they stopped short of endorsing it.

The Environmental Protection Agency on Friday formally declared carbon dioxide and five other heat-trapping gases to be pollutants that endanger public health and welfare, setting in motion a process that will lead to the regulation of the gases for the first time in the United States.

PORTLAND, Oregon: Senator John McCain sought to distance himself from President George W. Bush this week as he called for a mandatory limit on greenhouse gas emissions in the United States to combat climate change. McCain, in a speech on Monday at a wind power company, also pledged to work with the European Union to diplomatically engage China and India, two of the world's biggest polluters, if the nations refuse to participate in an international agreement to slow global warming.