President Biden moved Wednesday to protect more than 10 million acres of Alaska’s North Slope from development, barring oil drilling across giant swaths and canceling leases in the Arctic National Wildlife Refuge issued under President Donald Trump.

The conservation push covers nearly half of the National Petroleum Reserve-Alaska (NPR-A), the nation’s largest expanse of public land, which hosts a range of sensitive Arctic wildlife. It would impose a permanent ban on oil and gas development for 10.6 million acres of the reserve but would not block ConocoPhillips’s Willow project, which Biden approved there earlier this year and is poised to produce 576 million barrels of oil over the next three decades.

In a separate move, Interior Secretary Deb Haaland is canceling all seven outstanding leases the Trump administration awarded for oil exploration in the Arctic National Wildlife Refuge, in the state’s northeast corner. Drilling had been banned in the refuge, one of the nation’s most pristine natural areas, for decades until Congress ordered lease sales there in 2017. As a candidate, Biden pledged to undo those leases as part of his sweeping climate agenda.

In a statement, Biden said the state is full of “breathtaking natural wonders” that need protection.

“As the climate crisis warms the Arctic more than twice as fast as the rest of the world, we have a responsibility to protect this treasured region for all ages,” Biden said.

While the moves would do nothing to stop the Willow development - a top target of climate activists - it would ensure long-term protections for areas that provide vital wildlife habitat, said Chris Wood, president of the conservation group Trout Unlimited. He estimated that the federal government hasn’t set aside so many acres of land for conservation since the early 2000s.

“Conservation is a very long game and takes decades,” Wood said. “It’s rare to have these big-stroke opportunities. So it’s terrific and heartening to see the administration demonstrate they have a bit of a bold streak when it comes to protecting our lands and waters.”

Alaskan oil has complicated Biden’s attempt to enact aggressive measures to fight climate change. Oil advocates and industry analysts have said some areas of NPR-A are among the richest oil reserves available in the country, and Alaskan lawmakers have pushed development as a major source of jobs and revenue. But Biden had come to office promising “no more drilling on federal lands, period. Period, period, period.”

Alaska Oil and Gas Association President Kara Moriarty said in an email that the new Biden policies will make the United States more reliant on foreign oil, which could produce more planet-warming emissions than oil extracted in Alaska.

“The constant barrage of government regulation changes and whipsaws tells investors that Alaska is not a place to do business,” she said. That “makes no sense because Alaska has high environmental standards and some of the lowest emissions in the country.”

In March, Biden had approved Willow under intense political pressure. He said later he was compelled to because the company had legal leases for the area that predated his presidency.

But he announced that decision along with a plan to give “maximum protection,” a status authorized for Congress, for an additional 13 million acres in the reserve. Wednesday’s move makes that plan an official proposal, including requirements for environmental mitigation for 2.4 million acres where oil leasing can still happen there, and the ban on oil and gas leasing for the rest of it.

The proposal would also require reviews and public consultation every five years on whether to expand or designate new special areas for conservation in the reserve. The Bureau of Land Management will also be hosting public meetings about the proposal and taking public comment for 60 days before creating a final rule.

“We know that some of these places are irreplaceable treasures,” Haaland said in remarks to reporters. “Climate change is the crisis of our lifetime. . . . We must do everything within our control to care for and protect this fragile ecosystem.”

On the Arctic National Wildlife Refuge, Haaland said the lease sale under Trump was flawed, “based on a number of fundamental, legal deficiencies.” The Bureau of Land Management and the Fish and Wildlife Service have drafted a new analysis under Biden supporting that conclusion, administration officials said.

They found that Trump officials failed to meet requirements under the National Environmental Policy Act to analyze alternatives or to quantify greenhouse gas emissions from the development, administration officials said. That led Haaland to cancel the leases, administration officials said.

But Moriarty called the decision arbitrary, and Alaskan political leaders are likely to object to Interior’s legal justification. Many, including Sen. Lisa Murkowski (R), fought for decades to open up part of the region’s coastal plain for drilling, and inserted requirements to lease oil rights in the area as part of a 2017 tax law overhaul. Local officials who support drilling have called Biden’s attempts to undo the leases federal overreach.

At the same time, oil companies in recent years have also shown waning interest in the refuge and are more interested in the NPR-A. Regenerate Alaska, a division of an Australian firm, was the only oil company to directly acquire a tract on the refuge’s nearly 1.6 million-acre coastal plain, and it voluntarily canceled its lease in 2022, after Chevron and Hilcorp, two other major oil companies, had also jettisoned their claims.

The NPR-A, roughly the size of Indiana, was officially designated for oil and gas development by the Naval Petroleum Reserves Production Act in 1976. The law created special rules for oil and gas extraction and set aside some areas for “maximum protection” of the environment.

Today, the area remains a sizable reserve for domestic supplies of oil but has become increasingly prized as an Arctic wildland, offering key habitat for polar bears, migrating caribou and waterfowl.

Climate activists and many environmentalists were dismayed March 13, when the Biden administration approved the Willow project, which according to federal officials could produce 576 million barrels of oil over 30 years.

ConocoPhillips has held leases to develop oil as part of the Willow project since the late 1990s. After roughly five years of permitting and legal fights, the Biden administration approved the project to have as many as three drilling sites with up to 199 total wells. It shrank the project from the five pads ConocoPhillips had originally proposed following recommendations from a government review to keep development out of a yellow-billed loon nesting site and caribou migration paths.