Washington ? Riven by partisanship, the Senate plunged into a widely anticipated debate Monday over sweeping health care legislation that President Barack Obama and congressional Democrats have vowed to approve and Republicans have sworn to block.

Debate is expected to last for weeks over the legislation, which includes a first-time requirement for most Americans to carry insurance and a mandate for insurers to cover any paying customer regardless of medical history or condition.

“We must avoid the temptation to drown in distractions and distortions,” Senate Majority Leader Harry Reid said in the first moments of the first speech, a jab at Republicans that was reciprocated minutes later.

“Well, I don’t know what’s more preposterous: saying that this plan ‘saves Medicare’ or thinking that people will actually believe you,” Sen. Mitch McConnell of Kentucky, said of Reid’s oft-made statement.

At a cost of nearly $1 trillion, the legislation is designed to extend health care to millions of American who lack it, abolish insurance industry practices such as denying coverage based on pre-existing conditions and cut back on the rise of health care spending overall.

Despite its huge price tag, the Congressional Budget Office has estimated the 2,074-page bill would reduce federal deficits by $130 billion over the next decade. In all, CBO said 31 million uninsured individuals would receive insurance if the bill were enacted, many of them assisted by federal subsidies. As much as 94 percent of the eligible population would wind up covered. The legislation would be paid for through a combination of cuts in projected Medicare payments to hospitals and other providers, 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, Democrats struggling with their own internal divisions as well as Republican opposition.

Democrats control 60 seats in the Senate, precisely the number needed to trump a promised Republican filibuster. While Reid spent most of the day jousting with Republicans, his ability to steer the bill to passage will depend on finding ways to finesse controversial provisions within the measure. None is more important than calls for the government to sell insurance in competition with private firms. Liberals favor the plan; moderate and conservative Democrats oppose it. As drafted the bill establishes a so-called government option, although each state can block it.