Federal officials Thursday announced plans to expand two marine sanctuaries in a move that would permanently protect the entire Sonoma County coast and the southern third of Mendocino County's coast from oil and gas drilling and other environmental impacts.

The administrative step follows years of attempts by North Coast congressional representatives to protect the area through legislation. Retiring Rep. Lynn Woolsey said the expansion mirrored a proposal she introduced in 2004 but which failed to win final approval in the Republican controlled House of Representatives.

"This is a good day," Woolsey, the 10-term Democrat from Petaluma, said at a news conference in Washington, D.C. announcing the expansion plans. "At long last, we're on the road to giving these waters off the Sonoma County coast the protection they need and deserve."

Environmentalists, who have pushed for permanent protection of the area since the late 1970s and fought off drilling threats through a patchwork of annual moratoriums that lapsed in 2009, hailed the move as a historic accomplishment for their campaign.

"This is Santa arriving and landing on the beach," said Richard Charter, a senior fellow of the Ocean Foundation who has worked against oil drilling on the coast for four decades.

The expansion would push the existing Gulf of the Farallones and Cordell Bank national marine sanctuaries from Bodega Bay to just north of Point Arena on the Mendocino coast. The new area takes in more than 60 miles of coast and spans west to include almost 2,100 square nautical miles of ocean, an expanse larger than the state of Delaware, officials said.

The current Farallones and Cordell Bank boundaries encompass more than 1,360 square nautical miles and stretch from Bodega Bay south to just outside the Golden Gate of San Francisco Bay. They are managed by the National Oceanic and Atmospheric Administration, an agency under the Department of Commerce.

The expansion is subject to a NOAA study and public comment process that is set to begin in January and take 18 to 24 months, officials said.

As unveiled Thursday, the expansion would establish a chain of national marine sanctuaries from Mendocino County to Cambria, south of Big Sur in northern San Luis Obispo County.

The current sanctuaries were established by legislation and administrative action in the 1980s and 1990s. They allow fishing but are off limits to oil drilling and other commercial activities such seafloor mining and discharges by ocean liners.

Other California Democratic representatives who announced the expansion Thursday included Sen. Barbara Boxer, Rep Lois Capps, Rep. Sam Farr, Rep Jackie Speier and Rep. Barbara Lee.

You can reach Staff Writer Brett Wilkison at 521-5295 or brett.wilkison@pressdemocrat.com.