A stretch of the Pacific Ocean off California's wild north coast seems poised to get permanent federal protection from oil exploration and other development, in recognition that the area lies within one of the four richest marine feeding grounds in the world.

The US Senate is expected this week to vote in favor of extending two marine sanctuaries to cover ocean waters off a 76-mile stretch of the Sonoma County and south Mendocino County coasts – a move that would be a major victory for California in its 50-year battle to restrict offshore oil drilling. The House of Representatives approved the measure April 1.

"After decades of struggle, the door has opened to the national significance of this region," says Richard Charter of the environmental group Defenders of Wildlife. He says 25 years of give and take by oil interests, environmentalists, and politicians have finally aligned, even as public interest in beach protection is rising.

President Bush is likely to sign the bill because of its many supporters, including the National Oceanic and Atmospheric Administration, state and local governments, the fishing industry, conservation groups, and marine scientists, say close observers.

California's Mendocino-Sonoma region is probably best known for its onshore beauty: soaring redwoods, the rolling hills of wine country, a rugged coastline. But its offshore attributes are no less unique. The natural interaction of wind and water currents brings nutrients up from the ocean floor and distributes them along the California coast – providing sustenance for birds and marine life, including endangered salmon, Steller sea lions, gray whales, and northern fur seals.

A high-profile spill of 58,000 gallons of fuel oil from a tanker that struck the San Francisco Bay Bridge in November – closing fisheries, ending crab season, and fouling beaches – was an added catalyst to the legislation, Mr. Charter and others say. Several members of Congress whose districts were hit by the spill have become sponsors or supporters of the bill in recent months.

"They are more concerned because they've realized we really haven't gotten that much better in cleaning [oil spills] up," Charter says.

If the legislation is approved, it would double the size of two existing national marine sanctuaries near San Francisco and Marin, called Cordell Bank and Gulf of Farallones.

Before the House approved the measure, Republicans on the Natural Resources Committee had warned it would cut off access to potential future supplies of oil and gas, even as oil prices topped $100 per barrel.

"The industry is concerned about the overall issue of supply versus demand: Every drop of oil we can't produce domestically from US reserves is replaced by a drop of foreign imports," says Joe Sparano, president of the Western States Petroleum Association, a trade group. "But … we have respect for what appears to be a very strong and clear signal from the public."

Others note that California's opposition to offshore drilling puts more pressure on other domestic oil-producing regions, such as Alaska and the Gulf of Mexico. It's not known how much oil or gas could lie in the areas that would be newly protected.

"The standoff between environmentalism and energy realities is something this country will have to confront, not at the state level but the federal level, and not just about issues in California but in other areas of the country where we have oil," says Herb London, president of the Hudson Institute, a Washington think tank.

There has been scant new federal protection of ocean regions in recent years, notes William Moomaw, professor of international environmental policy at the Fletcher School of Tufts University, in Medford, Mass. The last significant move was in June 2006, when Mr. Bush signed a proclamation creating the Northwestern Hawaiian Islands Marine National Monument, which put 140,000 square miles of coral reef ecosystem under the nation's toughest marine environmental protection.

Enlarging the sanctuaries is of enormous importance to the well-being of the fishing industry, which has been socked by mounting fishing restrictions, says Zeke Grader, executive director of the Pacific Coast Federation of Fishermen's Associations.