WASHINGTON — The Interior Department on Thursday granted Royal Dutch Shell conditional approval of its plan to begin drilling exploratory wells in the Arctic Ocean next summer, a sign the Obama administration is easing a regulatory clampdown on offshore oil drilling that it imposed after last year's deadly accident in the Gulf of Mexico.

The move confirms a willingness by President Obama to approve expanded domestic oil and gas exploration in response to high gasoline prices and continuing high unemployment.

The decision to tentatively approve Shell's plan to drill four exploratory wells in the Beaufort Sea off the North Slope of Alaska represents a major step in the company's efforts to exploit the vast oil and gas resources under the Arctic Ocean, although some hurdles remain.

The company has spent nearly $4 billion and more than five years trying to win the right to drill in the frigid waters, against the opposition of many environmental advocates and of Alaska Natives who depend on the sea for their livelihoods.

Opponents say the harsh conditions there heighten the dangers of drilling and make cleaning up any potential spill vastly more complicated than in the comparatively benign waters of the Gulf.

Administration officials cautioned that the company must win a number of secondary permits before it can begin punching holes in the seabed. The plan approved Thursday, considered the overarching one, contains detailed information on how the company would respond to any blowout and spill.

"We base our decisions regarding energy exploration and development in the Arctic on the best scientific information available," said Michael Bromwich, director of the Bureau of Ocean Energy Management, Regulation and Enforcement, which oversees offshore drilling.

The plan is almost certain to face legal challenges.

"No drill bits are going to hit the Arctic seafloor until at least one, and probably several, courts have reviewed this plan," said Brendan Cummings, senior counsel at the Center for Biological Diversity, which is already suing to stop drilling in the Chukchi Sea west of Alaska.

Shell has proposed drilling four wells at a depth of approximately 160 feet of water about 20 miles from shore in the Beaufort.

The BP well that exploded in the Gulf in April 2010 was at a depth of more than 5,000 feet and 40 miles from the Louisiana coast. The accident killed 11 workers and spilled nearly 5 million barrels of oil into the Gulf.