WASHINGTON - There has been no more reliable cheerleader for President Obama's energy and climate change policies than Daniel J. Weiss of the left-leaning Center for American Progress.
But Mr. Obama's recent enthusiasm for nuclear power, including his budget proposal to triple federal loan guarantees for new nuclear reactors to $54 billion, was too much for Mr. Weiss.
The president's embrace of nuclear power was disappointing, and the wrong way to go about winning Republican votes, he said, adding that Mr. Obama should not be endorsing such a costly and potentially catastrophic energy alternative "as bait just to get talks started with pro-nuke senators."
The early optimism of environmental advocates that the policies of former President George W. Bush would be quickly swept away and replaced by a bright green future under Mr. Obama is for many environmentalists giving way to resignation, and in some cases, anger.
Mr. Obama moved quickly in his first months in office, producing a landmark deal on automobile emissions, an Environmental Protection Agency finding that greenhouse gases endanger public health and welfare, a virtual moratorium on oil drilling on public lands and House passage of a cap-and-trade bill.
Since then, in part because of the intense focus on the health care debate last year, action on environmental issues has slowed. The Senate has not yet begun debate on a comprehensive global warming bill, the Interior Department is writing new rules to open some public lands and waters to oil drilling and the E.P.A. is moving cautiously to apply the endangerment finding.
Environmental advocates largely remained silent late last year as Mr. Obama all but abandoned his quest for sweeping climate change legislation and began to reach out to Republicans to enact less ambitious clean energy measures.
But the grumbling of the greens has grown louder in recent weeks as Mr. Obama has embraced nuclear power, offshore oil drilling and "clean coal" as keystones of his energy policy. And some environmentalists have expressed concern that the president may be sacrificing too much to placate Republicans and the well-financed energy lobbies.
Erich Pica, president of Friends of the Earth, whose political arm endorsed Mr. Obama's candidacy for president, said that Mr. Obama's recent policy emphasis amounted to "unilateral disarmament."
"We were hopeful last year; he was saying all the right things," Mr. Pica said. "But now he has become a full-blown nuclear power proponent, a startling change over the last few months."
Mr. Obama said in his remarks on the nuclear project this week that he knew his policies were alienating some environmentalists.
"Now, there will be those that welcome this announcement, those who think it's been long overdue," Mr. Obama said of the new nuclear loan guarantee. "But there are also going to be those who strongly disagree with this announcement. The same has been true in other areas of our energy debate, from offshore drilling to putting a price on carbon pollution. But what I want to emphasize is this: Even when we have differences, we cannot allow those differences to prevent us from making progress."
Mr. Obama has long supported nuclear power, as a senator and as a candidate for president. Employees of the Exelon Corporation, the Chicago-based utility that is the largest operator of nuclear plants in the United States, have been among Mr. Obama's biggest campaign donors, giving more than $330,000 over his career, according to the Center for Responsive Politics.
In response to criticism of some of its energy policies, the White House points to its clean energy investments, including $80 billion in stimulus spending on energy-related projects, and its continuing support for comprehensive climate and energy legislation. But critics in the green movement say they wish the president would play a more active role in the climate debate.
"I think we all had higher hopes," said Bill Snape, senior counsel for the Center for Biological Diversity. "We expected a lot in the first year, and everyone agrees they didn't quite live up to it. But there is recognition that he and the whole administration will get another stab at it."
Mr. Snape said his group was particularly disappointed that the administration did not designate the polar bear as endangered by global warming and that it could not push a climate change bill through Congress.
"You can't get anything right," he said, "unless you get the polar bear right."
Frances Beinecke, president of the Natural Resources Defense Council, one of the administration's most stalwart supporters up to now, also expressed disappointment in the president's new focus on nuclear power and his mention in the State of the Union address of "clean coal technologies."
Mr. Obama was referring to the prospect of capturing and storing carbon dioxide emissions from coal-fired power plants, an as-yet-unproven technology. He was sending a signal to members of Congress from states that are dependent on mining coal or that burn it for electricity that any legislation he supported would accommodate their concerns.
"N.R.D.C. knows there is no such thing as ‘clean coal,' " Ms. Beinecke wrote in a blog post after the State of the Union address. "Every single step in the coal power cycle is dirty, from the profoundly destructive mountaintop removal mining to the smokestack emissions, which are responsible for 24,000 deaths a year."
Eric Haxthausen, the United States climate policy director for the Nature Conservancy, has generally supported the administration's goals and actions on energy and environment, although he said they fell short of what was needed to address global warming.
He said that Mr. Obama's pledge at the United Nations conference in Copenhagen on climate change to reduce American emissions by 17 percent by 2020 compared with 2005 levels had raised the stakes. The United States government is now on record promising the world that it will take major steps to reduce greenhouse gas pollution, Mr. Haxthausen said.
"What's needed to give this process life is a binding agent," he said, "some force to bring these things together, and the White House has to be intimately involved. The reality is there's a bit of a bully pulpit role that's needed, and the question is, will the administration deliver."