Obama's Climate Adviser, Carol Browner, to Depart White House

The White House energy and climate adviser is due to step down in the next few weeks, in a departure seen as the collapse of Barack Obama's ambitious green agenda.

Officials told reporters on Monday night that Carol Browner, who had served as the first White House energy and climate change "tsar", would be leaving and that she may not be replaced.

Reports of Browner's exit - barely 24 hours before Obama was to set out his priorities for the coming year in his state of the union address - reinforced concerns expressed by environmental groups that he was preparing further compromises on his once-ambitious green agenda to try to build a working arrangement with Republicans.

Obama has also come under pressure from the main business lobby, the Chamber of Commerce, which opposes environmental regulations.

But Browner's exit also recalled the extent to which Obama failed to realize his sweeping campaign promise of weaning America off fossil fuels, and making the transition to a new clean energy economy.

Browner, who headed the environmental protection agency during the Clinton administration, was seen as a shrewd operative, and was designated Obama's point person in the effort to enact climate change legislation.

With Democrats in control of both houses of Congress, environmental organizations in early 2009 saw reasonable prospects for the passage of comprehensive climate change legislation.

In Obama's first months in the White House, Browner presided over a complex set of negotiations with US car manufacturers to produce an agreement that would increase fuel efficiency by as much as 25% over the next five years.

She was also credited with giving Democratic leaders in Congress room to build support to pass a climate change bill through the house of representatives in June 2009. But the effort to pass cap and trade bill foundered in the Senate last year - with some Democrats blaming Obama for failing to send a strong enough signal that he was behind the bill. Others blamed the White House for choosing to move forward on health care reform before energy and climate change.

Since the Democrats' defeat in November's mid-term elections, Obama has said he will not seek to pass sweeping climate change legislation.

"I think there are a lot of Republicans that ran against the energy bill that passed in the House last year and so it's doubtful that you could get the votes to pass that through the House this year or next year or the year after," Obama told a post-election press conference.

Meanwhile, Republicans in the house were calling for an investigation of Browner's influence over the energy and climate agenda.

The EPA she once served was also in the firing line of Republicans, and some conservative Democrats, who are pushing to strip the agency of its authority to act on greenhouse gas emissions.

Browner's reputation also took a hit with the Obama administration's handling of the BP oil spill. In August, she made the now-notorious claim on behalf of the White House that the "vast majority" of the 4.9m barrels of oil that spewed into the Gulf of Mexico from BP's broken well was gone. Her statement was later discredited.

Even before reports of Browner's exit, environmental organizations had already been expressing fears that Obama was prepared to sacrifice his green agenda to his efforts to build a working relationship with Republicans.

More than 20 environmental and public health organizations wrote to Obama last week urging him to stand up for the EPA in his state of the union speech tonight.

The agency, which begun the process of regulating greenhouse gas emissions this year, has become the prime target for anti-government Republicans.

Republicans, along with Democrats from coal and oil states, are pushing to block the EPA from regulating greenhouse gas emissions, while environmental organizations want a commitment from Obama to use his presidential veto power to stop any such move.