WASHINGTON (AP) _ President Barack Obama's second-term energy agenda is taking shape and, despite the departure of key Cabinet officials, it looks a lot like the first: more reliance on renewable energy sources, such as wind and solar, and expanded production of oil and natural gas. Obama also is promising to address climate change, an issue he has acknowledged was sometimes overlooked during his first term.

``The president has been clear that tackling climate change and enhancing energy security will be among his top priorities in his second term,'' said Clark Stevens, a White House spokesman.

While the administration has made progress in developing renewable energy and improving fuel-efficiency standards for vehicles, ``we know there is more work to do,'' Stevens said.

He'll have to do that work with new heads of the agencies responsible for the environment. Interior Secretary Ken Salazar, Environmental Protection chief Lisa Jackson and Jane Lubchenco, head of the National Oceanic and Atmospheric Administration, have announced they are leaving. Energy Secretary Steven Chu is expected to follow his colleagues out the door in coming weeks.

The White House says no decisions have been made on replacements for any of the environment and energy jobs but says Obama's priorities will remain unchanged.

One of the first challenges Obama will face is an old problem: whether to approve the Keystone XL oil pipeline from Canada to Texas. Obama blocked the pipeline last year, citing uncertainty over the conduit's route through environmentally sensitive land in Nebraska. Gov. Dave Heineman is considering a new route; he is expected to make a decision next month.

The State Department has federal jurisdiction because the $7 billion pipeline begins in Canada.

The pipeline has become a flashpoint in a bitter partisan dispute. Republicans and many business groups say the project would help achieve energy independence for North America and create thousands of jobs.

But environmental groups have urged Obama to block the pipeline, which they say would transport ``dirty oil'' from tar sands in western Canada and produce heat-trapping gases that contribute to global warming. They also worry about a possible spill.

If the pipeline is approved, ``the administration would be actively supporting and encouraging the growth of an industry which has demonstrably serious effects on climate,'' 18 top climate scientists wrote in a letter to Obama this week.

Obama also faces a choice over whether to promote a boom in oil and natural gas production that has hampered growth of nontraditional energy sources such as wind and solar.

The emergence of cheap, plentiful natural gas in particular poses a dilemma for Obama, who supports gas development as a cleaner alternative to fossil fuels that trigger global warming.

Many environmental groups who support the president are wary of natural gas and are critical of drilling techniques such as hydraulic fracturing that allow drillers to gain access to reserves that formerly were out of reach. Hydraulic fracturing, also known as ``fracking,'' involves injection of water, sand and chemicals underground to break up dense rock that holds oil and gas.

The Obama administration has said it will for the first time require companies drilling for oil and natural gas on public and Indian lands to publicly disclose chemicals used in fracking operations. The proposed rules also would set standards for proper construction of wells and wastewater disposal.

Environmental groups are pushing the administration to do more to crack down on fracking, while industry groups and Republican lawmakers say federal rules are unnecessary, since states already regulate the drilling practice.

The natural gas boom ``puts the administration in an interesting position. They can be aggressive and look at natural gas for the possibilities it brings, or they can bow to the environmental community, which is not interested in more natural gas drilling,'' said Frank Maisano, a Washington spokesman for a range of energy producers from coal to wind.

The Environmental Protection Agency also is expected to forge ahead with the first limits on carbon pollution from coal-fired power plants. The administration has imposed rules on new plants but is expected to move forward on rules for existing plants, despite protests from industry and Republicans that new rules will raise electricity prices and kill off coal, the dominant U.S. energy source.

Older coal-fired power plants have been shutting down across the country, thanks to low natural gas prices and weaker demand for electricity.

Environmental groups also hope Obama will use his executive authority to protect more wild places, through creation of national monuments and other steps. The last Congress was the first since the 1960s not to designate a new wilderness area.

``We're hoping he can leave a legacy for conservation of public lands and have a real vision for it,'' said Jamie Williams, president of The Wilderness Society.

Michael Brune, executive director of the Sierra Club, said Obama's second term will be pivotal in the fight against climate change, which he called the ``singular issue of our time for anyone who cares about clean air, clean water and a safe future for our families.''

Brune urged Obama to take ``swift, decisive action to prevent more erratic weather, superstorms and wildfires.''

Top contenders to replace Salazar include former Washington Gov. Christine Gregoire, Deputy Interior Secretary David Hayes and John Berry, head of the Office of Personnel Management and a former director of the National Zoo. A host of green groups are backing Arizona Rep. Raul Grijalva.

Gregoire also is under consideration for the EPA slot, along with Jackson's deputy, Bob Perciasepe, and the head of the agency's air and radiation office, Gina McCarthy.

University of Maryland Prof. Donald Boesch, who served on Obama's 2010 oil spill commission, is a leading candidate to replace Lubchenco at NOAA.