WASHINGTON (CNN) -- Traditional Senate decorum yielded to brass-knuckle politicking in the health care debate Friday as top congressional Democrats sought to close party ranks before a key procedural vote this weekend.

Senate Democrats slammed their Republican colleagues as leaders of a counterproductive party of fear caught in an obstructionist mindset dating back to the New Deal. Republicans, in turn, ripped Democrats for pushing a bill that conservatives claim will force millions of Americans to drop insurance plans they like while jacking up premiums and doing nothing to slow spiraling medical costs.

The harsh rhetoric served as a backdrop for a rare Saturday night Senate vote on whether to formally proceed with floor debate on Senate Majority Leader Harry Reid's sweeping $848 billion health care bill.

If Republicans stay unified in opposition to the bill, Reid will need the support of all 58 Senate Democrats along with independent Sens. Bernie Sanders of Vermont and Joe Lieberman of Connecticut to reach the 60 votes necessary to overcome a filibuster.

"Those who want no reform, who want to keep the status quo for insurance companies, have thrown everything against the wall hoping something sticks," said Sen. Robert Menendez, D-New Jersey.

"All we hear is a dim echo of the past with no plan for the future," he argued. "They are the same fear mongering cries that went out when Franklin Roosevelt passed Social Security. ... It was all socialism. It was government hindering business from boosting the bottom line. It was all about fear."

Sen. Dick Durbin of Illinois, the number two Democrat in the Senate, dismissed GOP complaints about the length of the 2,074-page bill.

"The Republicans have come to the floor for weeks now decrying the fact that the bill we are presenting is long," he said. "The bill is long because we are tackling one-sixth of the American economy."

Durbin said he had "been searching in vain for the Republican health care bill."

"The Republicans have no alternative," he said. "They have no idea. The Republican health care reform bill is zero pages long because it provides zero relief."

GOP leaders gave as good as they got, repeatedly lambasting the majority for ramming through a bill Republicans insist will derail the country's economic future.

"Higher premiums, higher taxes on the middle class including small businesses, Medicare cuts ... .There's nothing here to like," said Sen. John Cornyn, R-Texas.

"In the words of the great Yogi Berra, this is deja vu all over again," declared Sen. John Thune, R-South Dakota.

Thune argued the bill was no different than previous failed Democratic attempts at reform. All of the Democrats' "pronouncements about deficit reduction (and) ... cost control aren't going to be found in this piece of legislation," he said.

Alaska GOP Sen. Lisa Murkowski seized on the recent controversial recommendation from a federal task force that women in their 40s should avoid routine mammograms.

"It's just kind of a peak under the curtain of what we can anticipate with a government-run program," she warned, despite Obama administration assurances that the task force's recommendation is advisory only and will not dictate policy.

The real action Friday, however, occurred behind closed doors as top Democrats worked to ensure a united caucus in advance of Saturday night's vote.

Two key Democratic moderates -- Sens. Mary Landrieu of Louisiana and Blanche Lincoln of Arkansas -- have refused to publicly indicate if they'll back Reid on Saturday night. Each has expressed concern about the cost and scope of the legislation.

A third Democratic moderate whose support had been in doubt -- Nebraska Sen. Ben Nelson -- said Friday he will vote to start debate.

"Throughout my Senate career I have consistently rejected efforts to obstruct," Nelson said in a written statement. "That's what (Saturday's) vote ... is all about."

Nelson stressed that his decision should not be construed to mean he would ultimately vote to pass the bill. "It is only to begin debate and an opportunity to make improvements," he said. "If you don't like a bill why block your own opportunity to amend it?"

According to Reid and other Democratic leaders, the controversial bill would extend health insurance coverage to at least 30 million additional Americans. They have cited an analysis by the non-partisan Congressional Budget Office for coverage and cost figures.

The CBO estimates the proposal would reduce the federal deficit by about $130 billion over the next 10 years, through 2019. Any effect on the deficit in the following decade would be "subject to substantial uncertainty," but probably would result in "small reductions in federal budget deficits," according to the CBO.

The bill includes a range of tax increases and new fees. The Medicare payroll tax on individuals earning $200,000 a year and couples earning $250,000 a year would increase by half a percentage point, from the current 1.45 percent to 1.95 percent. In addition, insurers providing costly health coverage -- known as "Cadillac" plans -- would face a 40 percent tax on policies worth more than $8,500 for individuals and $23,000 for families.

The bill also includes a 5 percent tax on the cost of elective cosmetic surgery, as well as new fees for insurers and pharmaceutical manufacturers. The total projected revenue raised by all the taxes and fees would exceed $200 billion.

The bill would require individuals to buy health insurance, with a fine for non-compliance of $95 in the first year that would escalate to $750 by 2016.

Unlike the plan recently passed by the House of Representatives -- which is projected to cost more than $1 trillion -- the Senate bill does not mandate that all employers offer health care. Businesses with more than 50 workers, where at least one employee qualifies for government subsidies, would face a penalty of $750 for every full-time employee if it does not offer health care coverage.

The Senate bill also would expand government-run Medicaid coverage for the poor to everyone making less than 133 percent of the national poverty level.

Democratic leaders in both chambers have been wrestling with the most contentious issues, including abortion and immigration, as well as how to pay for reform.

The House bill has more restrictive abortion language, and includes a 5.4 percent income tax surcharge on individuals making more than $500,000 and couples earning more than $1 million.

Both bills include a government-run public option, but the Senate version allows states to opt out before the national program would go into effect in 2014.

The two bills are virtually identical on a broad range of changes, including creating health insurance exchanges, expanding Medicaid, subsidizing insurance for low- and some middle-income families, and capping out-of-pocket medical expenses, while preventing insurance companies from denying coverage for pre-existing conditions.

Insurers under both plans would be barred from charging higher premiums based on a person's gender or medical history.

If the Senate eventually passes a bill, a congressional conference committee would need to merge the House and Senate proposals into a consensus version requiring final approval from each chamber before moving to Obama's desk to be signed into law.

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