WASHINGTON (AP) - Republican Sen. Olympia Snowe broke with her party Tuesday and said she will vote for a Democratic health care bill, handing President Barack Obama a much-sought boost in his quest to expand access to medical coverage to all Americans.

Approval of the legislation by the Senate Finance Committee was a foregone conclusion going into Tuesday's vote, since Democrats outnumber Republicans 13-10 on the panel. But Snowe's decision gave the vote a significance that transcends partisan divisions. For months, congressional Republicans have been virtually unanimous in denouncing the Democratic bills as an unwarranted expansion of government influence.

The Maine senator kept virtually all of Washington guessing about how she would vote until she announced it late in the Senate Finance Committee debate Tuesday. She told her colleagues she has misgivings about the bill, but "when history calls, history calls."

Democrats, aware that Snowe could be the only Republican in Congress to vote for their health care overhaul, have spent months addressing her concerns about making health care affordable and how to pay for it.

"Ours is a balanced plan that can pass the Senate," declared Finance Committee Chairman Max Baucus, D-Mont. Health care legislation is expected to be on the Senate floor the week after next, said a spokesman for Majority Leader Harry Reid of Nevada, who must combine the Finance version with a more liberal proposal from the health committee.

The expected approval by Baucus' committee would push a remake of the U.S. health care system closer to reality than it has been in decades. Four other congressional committees finished their work before August and for months all eyes have been on the Finance panel, the one whose moderate makeup most closely resembles the Senate as a whole.

The committee's centrist legislation is also seen as the best building block for a compromise plan that could find favor on the Senate floor. But nearly unanimous opposition from Republicans means a tough battle lies ahead.

Baucus' 10-year, $829-billion plan would, for the first time, require most Americans to purchase insurance and it also aims to hold down spiraling medical costs over the long term. Questions persist about whether it would truly provide access to affordable coverage, particularly for self employed people with solid middle class incomes.

Much work would lie ahead before a bill could arrive on Obama's desk, but action by the Finance Committee would mark a significant advance, capping numerous delays as Baucus held marathon negotiating sessions - ultimately unsuccessful - aimed at producing a bipartisan bill.

The Finance Committee's top Republican, Chuck Grassley of Iowa, gave voice to the GOP's concerns about the bill, saying it was "moving on a slippery slope to more and more government control of health care."

"There's a lot in this bill that's just a consensus that needs to be done, but there are other provisions of this bill that raise a lot of questions," Grassley said, contending the legislation would mean higher costs for Americans.

One of the biggest unanswered questions is whether the legislation would slow punishing increases in the nation's health care costs, particularly for the majority who now have coverage through employers. The insurance industry insists it would shift new costs onto those who have coverage.

Congressional Budget Office Director Douglas Elmendorf, under questioning by Republican senators, acknowledged that the bill's total impact on the nation's health care costs is still unknown. The CBO has been able to establish that the legislation would reduce federal government deficits, but Elmendorf said his staff has not had time to evaluate its effects on privately insured people. Government programs pay about half the nation's annual $2.5 trillion health care tab.

Once the Finance Committee has acted, the dealmaking can begin in earnest with Senate Majority Leader Harry Reid, D-Nev., working with White House staff, Baucus and others to blend the Finance bill with a more liberal version passed by the Health, Education, Labor and Pensions Committee.

Baucus' bill includes consumer protections such as limits on copays and deductibles and relies on federal subsidies to help lower-income families purchase coverage. Insurance companies would have to take all comers, and people could shop for insurance within new state marketplaces called exchanges.

Medicaid would be expanded, and though employers wouldn't be required to cover their workers, they'd have to pay a penalty for each employee who sought insurance with government subsidies. The bill is paid for by cuts to Medicare providers and new taxes on insurance companies and others.

Unlike the other health care bills in Congress, Baucus' would not allow the government to sell insurance in competition with private companies, a divisive element sought by liberals.

Last-minute changes made subsidies more generous and softened the penalties for those who don't comply with a proposed new mandate for everyone to buy insurance. The latter change drew the ire of the health insurance industry, which said that without a strong and enforceable requirement, not enough people would get insured and premiums would jump for everyone else.

A major question mark for Reid's negotiations is whether he will include some version of a so-called public plan in the merged bill. Across the Capitol, House Democratic leaders are working to finalize their bill, which does contain a public plan, and floor action is expected in both chambers in coming weeks. If passed, the legislation would then go to a conference committee to reconcile differences.

In a statement issued Tuesday afternoon, Maine Govenor John Baldacci, a Democrat, welcomed the news of Snowe's decision.

"When the light of history shines on political leaders, they can either move things forward or stand in the way of progress," Baldacci said in a prepared statement released by email. "Senator Snowe has recognized the important opportunity before this country to improve health care for all Americans. She has stepped up to address the challenges that remain ahead, and she is committed to doing the hard work to move forward."