By Patrick Rucker and Valerie Volcovici

WASHINGTON (Reuters) - President Barack Obama's State of the Union pledge to better manage fossil fuel development will face a test within days, when federal officials rule on whether to open public lands containing more than 600 million tons of coal to more mining.

Interior Department officials are due to decide Jan. 27 on whether to lease two mine sites on federal land in Wyoming's coal-rich Powder River Basin, where the black rock runs in 10-story seams.

Environmentalists strongly oppose more coal mining on federal land, saying burning all that coal would exacerbate climate change. Reforming government controls on federal lands is one of the few actions still available to Obama in his final year in office.

Developing the two Wyoming sites would make more than 640 million tons of coal available to mining companies, according to the Interior Department. Each ton of burned coal creates 1.66 metric tons of carbon dioxide, according to government data.

That means burning all the coal at the lease sites would add more than a billion metric tons of carbon dioxide to the atmosphere.

The Energy Information Administration says roughly 41 percent of U.S. coal production occurs on federal land, and environmentalists have argued strongly against permitting more mining there.

The Interior Department must assess the environmental impact of each energy lease under a law enacted during the 1970s under President Richard Nixon, decades before climate change became a concern to policymakers. Conservationists say those environmental studies should account for the wider climate impact.

In his State of the Union address on Tuesday, Obama vowed to "change the way we manage our oil and coal resources, so that they better reflect the costs they impose on taxpayers and our planet."

In Obama's first term, the Interior Department mulled but balked at raising royalty rates on companies that tap federal land.

Since then, environmentalists have urged the White House to undertake a sweeping review of fossil fuel extraction. In the meantime, they have called on the administration to refrain from awarding further leases, including the two in Wyoming.

"Until the administration steps back and considers all the impacts, we need a moratorium," said Jeremy Nichols of WildEarth Guardians which joined several other conservation groups in a letter on Wednesday urging Obama to freeze coal leases.

The two leases under consideration are West Antelope III and Decker South, which abut existing mines. The administration has not indicated its position on those two leases, and the Interior Department on Wednesday declined to comment.

Interior Secretary Sally Jewell visited western states last summer, calling for "an honest and open conversation about modernizing the federal government's coal program."

Last year, Obama used his authority to help secure a global climate agreement between nearly 200 countries. He also denied a permit to build the Keystone XL oil pipeline and issued new rules to crack down on carbon pollution from U.S. power plants.

In coming weeks, the Interior Department’s Bureau of Land Management is also expected to release a plan to curb emissions from oil and gas production on federal land.

"This is the obvious low-hanging fruit on climate change that he hasn’t touched yet," said a Congressional aide who tracks the administration's coal policies.

To Learn More:

Why is Congress Turning over Public Lands to Foreign Copper Mine Companies? (by Noel Brinkerhoff, AllGov)

Lawsuit Aims at Environmental Impact of U.S. Coal-Leasing Program (by Noel Brinkerhoff and Steve Straehley, AllGov)

Coal Mines Escape Regulation of Methane Emissions (by Matt Bewig, AllGov)

Federal Judge Orders Bureau of Land Management to Divulge Names of Oil and Gas Lease Bidders (by Matt Bewig, AllGov)