The company’s plans were set back again at the end of December 2010 when an E.P.A. panel revoked the air pollution permit for one of its drilling rigs. That infuriated Shell executives, frustrated White House officials and unleashed the ire of Alaska’s two senators, who introduced legislation to streamline permitting.

The E.P.A. action effectively stopped Shell’s plans for another year, but the president put his foot on the gas.

In May 2011, he authorized onshore oil lease sales in Alaska’s National Petroleum Reserve and extended oil companies’ offshore leases in the Arctic Ocean. In July, he created by executive order a multiagency task force led by the deputy interior secretary but overseen by Ms. Zichal to prod the bureaucracy on Arctic issues, particularly Shell’s drilling plans.

Still, some government officials complained that there remained huge gaps in response plans for a spill and too many unknowns about the effect of drilling on marine animals.

The commandant of the Coast Guard, Admiral Robert J. Papp Jr., went public last August, warning Congress that the country was woefully unprepared to respond to a major spill in the Arctic. That same month, Ms. Beinecke, president of the Natural Resources Defense Council and a member of the BP spill commission, urged the president to block Arctic drilling. “The administration should put on the brakes,” she wrote in an Op-Ed article in The New York Times.

The commission’s final report said that for Arctic drilling to be done safely, “both industry and government will have to demonstrate standards and a level of performance higher than they have ever achieved before.”

But these warnings did not slow progress. At the urging of regulators, Shell strengthened spill prevention and response plans. It built a containment system for the Arctic modeled on the one that successfully capped the BP well and added ships and equipment to the armada to be in place to capture any spilled oil. The company agreed reluctantly to shorten its Chukchi Sea drilling season by 38 days, to less than three months, to ensure that the area would be ice-free in case of a blowout.