The Obama-imposed leasing prohibitions "will remain in full force and effect unless and until revoked by Congress," says judge

ANCHORAGE, Alaska, March 30 (Reuters) - A federal judge in Alaska has overturned U.S. President Donald Trump's attempt to open vast areas of the Arctic and Atlantic oceans to oil and gas leasing.

The decision issued late Friday by U.S. District Court Judge Sharon Gleason leaves intact President Barack Obama's policies putting the Arctic's Chukchi Sea, part of the Arctic's Beaufort Sea and a large swath of Atlantic Ocean off the U.S. East Coast off-limits to oil leasing.

Trump's attempt to undo Obama's protections was "unlawful" and a violation of the federal Outer Continental Shelf Lands Act, Gleason ruled. Presidents have the power under that law to withdraw areas from the national oil and gas leasing program, as Obama did, but only Congress has the power to add areas to the leasing program, she said.

The Obama-imposed leasing prohibitions "will remain in full force and effect unless and until revoked by Congress," Gleason said in her ruling.

Trump's move to put offshore Arctic and Atlantic areas back into play for oil development came in a 2017 executive order that was part of his "energy dominance" agenda. The order was among a series of actions that jettisoned Obama administration environmental and climate-change initiatives.

The Trump administration has proposed a vastly expanded offshore oil leasing program to start this year. The five-year Trump leasing program would offer two lease sales a year in Arctic waters and at least two lease sales a year in the Atlantic. The Trump plan also calls for several lease sales in remote marine areas off Alaska, like the southern Bering Sea, that are considered to hold negligible potential for oil.

Obama had pulled much of the Arctic off the auction block following a troubled offshore Arctic exploration program pursued by Royal Dutch Shell. Shell spent at least $7 billion trying to explore the Chukchi and part of the Beaufort. The company wrecked one of its drill ships in a grounding and managed to complete only one well to depth. It abandoned the program in 2015 and relinquished its leases.

Gleason, in a separate case, delivered another decision Friday that blocks the Trump administration's effort to overturn an Obama-era environmental decision.

Gleason struck down a land trade intended to clear the way for a road to be built though sensitive wetlands in Alaska's Izembek National Wildlife Refuge. The Obama administration, after a four-year environmental impact statement process, determined that the land trade and road would cause too much harm to the refuge to be justified. Trump's then Interior Secretary Ryan Zinke broke the law when he summarily reversed the Obama policy without addressing the facts found in the previous administration's study of the issue, Gleason ruled. (Reporting by Yereth Rosen in Anchorage, Alaska Editing by James Dalgleish)

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