The new strategy  the result of more than a year of work by Interior Secretary Ken Salazar  also confronts an essential political reality: the Senate will insist on offshore drilling as part of a broader bill, expected after Easter, addressing climate change and other energy-related problems. Mr. Obama is trying to anticipate and shape that discussion by identifying areas that he thinks can responsibly be opened for exploration while quarantining others.

Nearly all of America’s coastal waters have been up for grabs since 2008 when President George W. Bush lifted a longstanding presidential moratorium on drilling in the outer continental shelf. A few months later, Congress allowed a parallel Congressional moratorium to expire. Mr. Bush also lifted a separate moratorium on drilling in Alaska’s Bristol Bay that was imposed by his father in 1990 after the Exxon Valdez spill. Bristol Bay is home to America’s richest fishing grounds and is the main driver of a $2.2 billion regional fishing industry.

Under the Obama administration’s plan, Bristol Bay will once again be completely protected, which is wonderful news. Further north in Arctic waters, the plan would allow drilling on existing leases in relatively small areas of the Chukchi and Beaufort Seas to proceed  which seemed inevitable, given legal and economic obstacles to reversing them. It would, however, postpone any further development pending the outcome of detailed scientific and environmental studies. Alaska’s environmentalists were encouraged, and they should be.

The rest of the plan is as significant for the areas it protects as for those it opens. Exploration will not be allowed on the Pacific Coast or along the Atlantic Coast north of Delaware. Seismic exploration  which in effect means exploratory drilling  will be allowed along the central and southern Atlantic Coast from Delaware to Florida, but, again, no new leases will be granted until the scoping process and the environmental reviews are finished.

The Interior Department’s seismic information is decades old, and one important point of the new plan is to discover what’s out there. The department’s most optimistic present estimate of the resources in the areas covered by the plan, including the Gulf of Mexico, is 63 billion barrels of economically recoverable oil.