Democrats called it a historic opportunity. Republicans called it a sham.

Long-awaited debate over President Barack Obama’s health care overhaul kicked off in the Senate with lawmakers trading bitter partisan words over the measure to remake one-sixth of the U.S. economy.

The legislative struggle is expected to last for weeks in a test that pits Republican senators determined not to give ground against Senate Democrats determined to deliver on Obama’s top domestic policy priority.

The 10—year, nearly $1 trillion legislation includes a first-time requirement for most Americans to carry insurance, greatly expands the Medicaid federal-state insurance program for the poor, and would require insurers to cover any paying customer regardless of their medical history or condition.

On Monday each side offered the first of what are likely to be dozens of amendments, with the measures seemingly designed as much to court a sceptical public as to reshape Senate Majority Leader Harry Reid’s 2,074-page bill.

“There’s not an issue more important than finishing this legislation,” Reid told his colleagues in putting them on notice for Saturday and Sunday sessions in December.

Reid said exorbitant health care costs have forced thousands of Americans into bankruptcy, creating an economic crisis that Congress must address.

Tens of millions of Americans lack health insurance or are underinsured, either because their employers do not provide it or they are out of work. The United States is the only developed nation that does not have a comprehensive national health care plan.

However, Republican Leader Mitch McConnell said the $979 billion, 10-year Senate bill is too expensive for a nation struggling financially.

“The notion that we would even consider spending trillions of dollars we don’t have in a way that the majority of Americans don’t even want is proof that this health care bill is out of touch,” McConnell said.

Arizona Sen. John McCain, the 2008 Republican presidential candidate, attacked the legislation as a “monstrosity” that employs “Bernie Madoff accounting, Enron accounting” as he offered the first Republican amendment. McCain’s amendment would strip out more than $400 billion in Medicare cuts to home health providers, hospitals, hospices and others -- a pitch to seniors, who polls show have deep concerns about the legislation.

Democrats planned to go on the offense on the same issue Tuesday with an amendment underscoring benefits to seniors and guaranteeing that basic Medicare benefits would not be touched.

Votes on amendments are expected to begin Tuesday. “We have an historic need and we have an historic opportunity. We have an opportunity to enact groundbreaking reform that will finally rein in the cost of health care,” said Sen. Max Baucus, a Montana Democrat.

The Congressional Budget Office has estimated that 31 million uninsured individuals would receive insurance if the bill were enacted, many of them assisted by federal subsidies. The legislation would be paid for through a combination of cuts in projected Medicare payments, a payroll tax on the wealthy and taxes on drug makers, medical device manufacturers, owners of high-cost insurance and others.

It has taken months to advance the legislation to the floor, as Democrats struggled with their own internal divisions as well as unanimous Republican opposition.

Democrats control 60 seats in the Senate, precisely the number needed to end a promised Republican filibuster, a legislative manoeuvre used to block a final vote on a bill. Reid’s ability to steer the bill to passage will depend on finding ways to finesse controversial provisions within the measure, such as a proposal for the government to sell insurance in competition with private firms.

Despite the public jousting significant action was occurring behind the scenes Monday evening as Reid and Baucus huddled to plot strategy with top White House and Cabinet officials including Chief of Staff Rahm Emanuel, Interior Secretary Ken Salazar and Health and Human Services Secretary Kathleen Sebelius, along with former Senate Democratic Leader Tom Daschle, Obama’s first pick for HHS secretary before his nomination was derailed by tax issues.

Liberals favour the government insurance plan; moderate and conservative Democrats oppose it. As drafted the bill establishes a so-called government option, although each state can opt out of it. Legislation passed earlier by the House also has a government option, with no state opt-out provision; it would have to be reconciled with any Senate-passed measure before a final bill could go to Obama’s desk.

Some Democratic senators say they won’t vote for the final bill without tighter restrictions on abortion coverage.

Coinciding with the start of debate, congressional budget experts said the bill would lower the average price of insurance premiums if it passes, although millions would face higher costs.

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