WASHINGTON — In a rare Sunday session, the Senate advanced legislation that would set aside more than 2 million acres in nine states as wilderness. Majority Democrats assembled more than enough votes to overcome GOP stalling tactics in an early showdown for the new Congress.

Republicans complained that Democrats did not allow amendments on the massive bill, which calls for the largest expansion of wilderness protection in 25 years. But Senate Majority Leader Harry Reid, D-Nev., and other Democrats said the bill — a holdover from last year — was carefully written and included measures sponsored by both Republicans and Democrats.

By a 66-12 vote, with only 59 needed to limit debate, lawmakers agreed to clear away procedural hurdles despite partisan wrangling that had threatened pledges by leaders to work cooperatively as the new Obama administration takes office. Senate approval is expected later this week. Supporters hope the House will follow suit.

“Today is a great day for America’s public lands,” said the bill’s sponsor, Sen. Jeff Bingaman, D-N.M. “This big, bipartisan package of bills represents years of work by senators from many states, and both parties, in cooperation with local communities, to enhance places that make America so special.”

The measure — actually a collection of about 160 bills — would confer the government’s highest level of protection on land ranging from California’s Sierra Nevada mountain range to Oregon’s Mount Hood, Rocky Mountain National Park in Colorado and parts of the Jefferson National Forest in Virginia. Land in Idaho’s Owyhee canyons, Pictured Rocks National Lakeshore in Michigan and Zion National Park in Utah also would be designated as wilderness.

Besides new wilderness designations, the bill would designate the childhood home of former President Bill Clinton in Hope, Ark., as a national historic site and expand protections for dozens of national parks, rivers and water resources.

Reid said about half the bills in the lands package were sponsored by Republicans. Most had been considered for more than a year.

“I am happy that after months of delay we will finally be moving forward,” Reid said.

The bill’s chief opponent, Sen. Tom Coburn, R-Okla., denounced what he called Democratic bullying tactics.

“I am disappointed the Senate majority leader has refused to allow senators the opportunity to improve, amend or eliminate any of the questionable provisions in his omnibus lands bill,” Coburn told fellow senators.

“When the American people asked Congress to set a new tone, I don’t believe refusing to listen to the concerns of others was what they had in mind,” Coburn said. “The American people expect us hold open, civil and thorough debates on costly legislation, not ram through 1,300-page bills when few are watching.”

Coburn and several other Republicans complained that bill was loaded with pet projects and prevented development of oil and gas on federal lands, which they said would deepen the nation’s dependence on foreign oil.

Environmental groups said the bill set the right tone for the new Congress.

“By voting to protect mountains and pristine wildlands, Congress is starting out on the right foot,” said Christy Goldfuss of Environment America, an advocacy group. “This Congress is serious about protecting the environment and the outstanding lands that Americans treasure.”