President Barack Obama"s U.S. healthcare overhaul plan has cleared an important Senate hurdle but lawmakers warned on Sunday of challenges ahead in winning support for passage, even among Obama"s own Democrats, according to Reuters. On Saturday, Senate Democrats gathered the 60 votes needed to open floor debate on the plan, which would make the biggest changes in the $2.5 trillion healthcare system in 40 years. It is the Obama administration"s top domestic policy initiative. No Republicans backed the procedural motion and a handful of conservative Democrats, whose votes were crucial, supported the floor debate but remained uncommitted to the bill itself. One of those was Democratic Senator Ben Nelson, who said on Sunday that he could not support the plan without big changes. "If there are a whole host of other items that are the same as they are right now, I wouldn"t vote to get it off the floor," Nelson said on the ABC"s "This Week" news program. Independent Senator Joseph Lieberman, usually an ally of the majority Democrats, said he could not support the bill either if the "public option" -- for a government-run health insurance plan to compete with private firms -- stays in the bill. "I don"t think anybody feels this bill ... will pass" as written, Lieberman said on NBC"s "Meet the Press" program. Debate will begin on Nov. 30 and is expected to last at least three weeks. The "public option" component of the bill is negotiable, Senator Richard Durbin, the Senate"s No. 2 Democrat, said on NBC on Sunday, adding the Senate bill "must" get passed by the end of 2009. If it goes into 2010, with other issues such as financial regulation reform and mid-term elections vying for attention, "it gets more complex," he said. "We"re anxious to get it done." The House of Representatives has passed its own version. Differences between Senate and House versions would have to be reconciled in January before Obama could sign a final measure. Senate Democratic Leader Harry Reid said it was wrong to link healthcare legislation and Monday"s controversial recommendation by an independent task force against routine mammograms for women in their 40s. "Republicans who deliberately conflate or confuse the two only confirm just how desperate they are to distract the American people from the real debate -- and from the fact that they have no vision for fixing our broken health care system. "There will be nothing in our bill to discourage or prohibit preventive treatments -- quite the opposite, in fact. And as a result, our historic reforms, like mammograms, will save lives," he said. The Senate bill would expand coverage to millions of the uninsured and it would bar insurers from denying coverage over preexisting conditions. It also would require virtually all Americans to buy insurance and set up exchanges to shop for healthcare coverage. "CADILLAC PLAN" TAX While offering subsidies to help low-income workers afford coverage, the plan also would raise the payroll tax on high-income workers that finances the Medicare system that provides for the elderly. It also would impose a tax on high-cost "Cadillac" insurance plans. Republicans have vowed to delay or block the bill, which they say is a costly government intrusion in the private sector that would raise premiums, reduce choices and increase taxes. "The bill is fundamentally flawed ... It puts big costs onto states," said Republican Senator Lamar Alexander on the "Fox News Sunday" program. "If the American people know that, the bill will collapse of its own weight." Pharmaceutical companies such as Pfizer Inc and Merck & Co Inc and insurers such as UnitedHealth Group Inc and WellPoint Inc are spending hundreds of millions of dollars on lobbying to influence lawmakers" views on reshaping an industry that fuels one-sixth of the economy. "The insurance industry is about the most highly concentrated industry in the country," said Democratic Senator Charles Schumer on CBS"s "Face the Nation." "So you need to inject some competition into the insurance industry. "The best way to do that is a public option. And the program that we"ve put together is set up by the government but then it"s on its own. There is no intent for it to compete unfairly against private insurance," he said. Democratic Senator Sherrod Brown said he would seek amendments that would allow the government to negotiate prices for Medicare prescription drugs for the elderly, would permit reimportation of drugs from low-cost countries and would seek to cut brand-name biotechnology drug prices.