President Barack Obama began his second term with a ringing pledge to tackle climate change — saying that “the failure to do so would betray our children and future generations.”

Four months later, everyone’s still waiting.

Instead of taking bold steps, Obama’s environmental regulators are dodging questions about how they intend to rein in the nation’s largest sources of greenhouse gases. They missed a major deadline last month for rolling out rules for future power plants, prompting environmental groups and several states to threaten lawsuits. And the EPA has insisted to Congress that it’s not even working on regulations for the next piece of the carbon puzzle — the nation’s vast fleet of existing power plants.

Meanwhile, signs are growing that the administration is poised to approve the Keystone XL oil pipeline from Canada, despite pleas from his green activist supporters.

Climate advocates say they still believe the president’s heart is in their cause, and they’re looking for him to use his executive authority to bypass a long-stalemated Congress. But they’ve also watched issue after issue compete for the White House’s attention this year — from gun control, budget cuts and immigration to Syria, Benghazi and the IRS. And they fear Obama is already running out of time.

Given the complexity of addressing greenhouse gas pollution across the U.S. economy and the usual long haul of the regulatory and judicial process, Obama’s window for taking action will shut soon, advocates fret. Wait too long, they say, and the next president will be making the final call.

“Every day, more sand passes through the hourglass of this administration,” said David Doniger, climate policy director at the Natural Resources Defense Council.

Doniger and others who follow the issue say crafting the complex regulations needed to make a serious dent in carbon pollution could take every moment left in Obama’s presidency, along with considerable use of his bully pulpit. The administration needs to make it clear that “this has the backing of the man at the top,” Doniger said.

“There needs to be a public plan,” he said. “There needs to be a schedule — what’s going to get done and when.”

“It’s going to be a long conversation, so he should get started,” said Eric Pooley, the Environmental Defense Fund’s senior vice president for strategy and communications.

Despite the lack of obvious action on a second-term climate agenda, advocates closest to the administration say Obama means what he says.

“President Obama is absolutely committed to tackling climate change,” said Carol Browner, Obama’s former top energy and climate adviser, who is now a senior fellow at the Center for American Progress. “This is a legacy issue for him that he really believes in.”

Supporters point to progress Obama made his first term, when he got the auto industry to agree to greenhouse gas limits for cars and approved $90 billion in stimulus spending for clean-energy projects, including some of the world’s largest wind and solar initiatives. The president’s actions on climate have been “historic,” White House spokesman Clark Stevens said.

Still, what’s missing is the heart of a climate strategy. And ever since Obama’s cap-and-trade proposal died in Congress three years ago, it’s been clear that the strategy will hinge on the EPA.

The agency has a powerful legal weapon: a 2007 Supreme Court decision that said EPA can regulate greenhouse gases under the Clean Air Act. But these days, it’s offering no public signs it’s leading the charge.

In April, EPA missed its legal deadline to finish writing a long-expected rule to limit greenhouse gases from future power plants — a lapse that prompted cities, states and environmental groups to file notice they intend to sue the agency. Pressed for details, EPA says only that after more than a year, it’s still “reviewing comments” on the rule. The agency did not respond to requests for comment on this story.

Meanwhile, the agency has told Republican lawmakers it’s not yet working on the crucial next step, a wide-ranging regulation that would limit carbon emissions from existing power plants. Those plants are EPA’s biggest target — they put out 2.2 billion tons of carbon dioxide a year, about 40 percent of the nation’s greenhouse gas emissions.

“The agency is not currently developing any existing source [greenhouse gas] regulations,” EPA air chief Gina McCarthy — Obama’s nominee for agency administrator — wrote in response to questions from Sen. David Vitter (R-La.).

The White House even scrubbed its draft new-plant rule last year to remove numerous mentions of plans to tackle existing plants.

EPA is also fighting a lawsuit by New York University’s Institute for Policy Integrity, which wants to force the agency to regulate greenhouse gas emissions from cars already on the road, which produce about 27 percent of U.S. carbon emissions.

In addition, EPA has declined to directly regulate methane emissions from oil and gas drilling operations, and last month acting Administrator Bob Perciasepe rejected a petition by environmentalists who wanted the agency to regulate methane emissions from coal mines. He cited “limited resources and ongoing budget uncertainties.”

No major action on climate is likely until after the Senate confirms McCarthy. But she’s run into a brick wall among Republicans, who stalled a committee vote on her nomination and may filibuster her on the floor.

McCarthy’s woes have had “a chilling effect on the administration’s desire to go forward on bold actions,” the Sierra Club’s Melinda Pierce said. “They don’t want to be lighting a fire out there before Gina is confirmed.”

Even if McCarthy makes it, the agency will still be short on Senate-confirmed leaders for its air and general counsel offices, among others, which many agency-watchers say could hamper progress on new regulations.

On top of that, activists are increasingly frustrated by signs the administration will green-light Keystone, despite warnings from some scientists that the pipeline could drive a huge release of carbon dioxide from Canada’s oil sands.

“If a second-term president after the hottest year in history, the biggest city inundated by flooding following a devastating hurricane … can’t make even a gesture as easy as stopping one pipeline to Canada, one has to wonder when exactly we’re going to see serious action,” said Bill McKibben, an activist who has organized mass sit-ins outside the White House to protest Keystone.

If activists’ expectations for Obama are high, it’s because he went out of his way to raise them.

He gave the climate a significant nod in his second inaugural address on Jan. 21, proclaiming that “some may still deny the overwhelming judgment of science, but none can avoid the devastating impact of raging fires and crippling drought and more powerful storms.”

In February’s State of the Union address, Obama vowed that “if Congress won’t act soon to protect future generations, I will.”

Environmentalists need to recognize that meeting those promises will take time, said Daniel J. Weiss, the Center for American Progress’s director of climate strategy, adding that a hastily written regulation could backfire during the inevitable court challenges. “A very poorly decided case won by big coal could send the administration back to the drawing board, and they want to avoid that,” he said.

“There are plenty of places to criticize” the administration’s efforts, said Council on Foreign Relations climate and energy expert Michael Levi. “But I don’t think that the fact that they haven’t announced a grand plan for this term is a great failure.”

A major obstacle has been the freeze on climate action on Capitol Hill, where cap and trade died in the Senate in 2010. Since then, Obama has looked for ways to “make some real changes” using his own authority, Vice President Joe Biden told Rolling Stone for an interview published this month.

“In the meantime, the president is going to use his executive authority to, essentially, clean up the bad stuff, encourage the good stuff and promote private industry moving in that direction,” Biden said.

Obama has also made a nonbinding international commitment to reduce U.S. greenhouse gas emissions by 17 percent from 2005 levels by 2020, with a future goal of 83 percent reduction by 2050. The U.S. and other nations are expected to agree to further steps in a new agreement scheduled to be completed in 2015.

The U.S. has inched close to its 2020 goal, partly because of the recession and related dips in energy use. But long-term cuts in greenhouse gas pollution will depend on reining in major sources like power plants, followed by targeting emissions from oil and gas producers.

Finishing the rule for new power plants, then moving on to existing plants, is greens’ “No. 1 policy goal for the second term,” EDF’s Pooley said.

Some observers have speculated that EPA could reach a deal with the power industry to reduce emissions, similar to the agreement it made with automakers. But power plant regulations would be far more complicated, many attorneys following the process say, and the electric industry is larger, more diverse and less willing to cooperate with the administration than the car companies were.

Eventually, observers like Levi said, Congress will need to step in with something like cap and trade or a carbon tax — two means of offering economic incentives for polluters to clean up.

For the time being, though, the onus will be on Obama to act where he can, activist McKibben said.

“He has a free throw,” McKibben said. “We don’t expect him to dunk over the GOP leadership in Congress, but we do expect that when he has an open shot to take, he takes it.”