The Arctic National Wildlife Refuge in northeast Alaska consists of 19 million acres — including a 1.5 million acre coastal plain seen as the potential source of at least 7.7 billion barrels of technically recoverable oil.

But in addition to reservoirs of untapped oil, the coastal plain is home to caribou, grizzly bears, wolves, migratory birds and threatened polar bears, and it has been labeled by conservationists as “America’s Serengeti.”

The conflict between advocates of developing the area’s bountiful energy resources and supporters of preserving the diverse wildlife has raged in Congress for decades. Here are some milestones of the long-running fight:

1980: President Jimmy Carter signs the Alaska National Interest Lands Conservation Act (PL 96-487) into law. The act designates the Arctic National Wildlife Refuge, requires a study of energy resources in the coastal plain and requires congressional approval for any future oil and gas development there.

1984-1985: An oil industry consortium conducts a seismic study of ANWR’s coastal plain, providing the basis for the mean estimate that 7.7 billion barrels of oil are technically recoverable.

1987: Based on those findings, the Reagan administration recommends that Congress approve leases to drill in the coastal plains. The Senate moves to do so two years later.

1989: A bill to allow drilling in ANWR advances in Congress until the Exxon Valdez oil spill dumps hundreds of thousands of barrels of crude oil in Prince William Sound — halting political momentum and giving opponents new ammunition.

1996: The Republican-controlled Congress passes a budget reconciliation bill that allows drilling in ANWR, but President Bill Clinton vetoes it.

2005: A provision allowing drilling in ANWR is included in the House-passed energy bill but dropped in conference with the Senate. The Republican-controlled Senate includes an ANWR drilling provision in its fiscal 2006 budget resolution, but it is dropped during the reconciliation process. An effort by Senate Appropriations Chairman Ted Stevens, R-Alaska, to add the ANWR provision to the defense spending bill is defeated.

2010: The U.S. Fish and Wildlife Service designates a large part of northern Alaska, including the coastal plain, as critical habitat, increasing the federal role in any potential energy development there.

2013: The Fish and Wildlife Service is expected to release a final comprehensive conservation plan for ANWR, which would update the one finalized by the Reagan administration in the 1980s. The revised plan is likely to recommend that Congress designate the coastal plain as wilderness, permanently taking it off-limits to oil and gas development.