WASHINGTON, Nov. 16 — Republican leaders began an intensive campaign on Sunday to sell their new agreement on Medicare drug benefits, racing to push the legislation through Congress over the objections of leading Democrats.
Senator Edward M. Kennedy, Democrat of Massachusetts, predicted that the measure as it now stands would not be approved by the Senate.
But President Bush hailed the agreement and said he would be "actively pushing the bill," one of his domestic priorities as he heads into a re-election year in which elderly voters are considered critically important.
Republican leaders said they were also counting on support from a powerful coalition of business and health care groups, as well as from AARP, the huge lobby for older Americans. John C. Rother, policy director of AARP, said Sunday that his view of the agreement was "generally favorable," though he wanted to see more details.
Senator Bill Frist, Republican of Tennessee, the Senate majority leader, expressed confidence that Medicare drug benefits would soon become a reality after "six years of empty promises, stalled negotiations and partisan gridlock."
Finally, Dr. Frist declared, the 40 million Medicare beneficiaries will be able to say: "Congress has delivered. Our government has delivered. Our president has delivered."
The continuing struggle over the legislation, which calls for the biggest expansion of Medicare in its 38-year history, is expected to highlight once again the profound ideological divisions over the future of the program.
Some influential Democrats vowed to fight the legislation, saying it would severely undermine the traditional government-run Medicare program, which serves more than 85 percent of the 40 million beneficiaries.
"I don't think that bill will pass the United States Senate," Mr. Kennedy said on the CBS News program "Face the Nation."
The Senate Democratic leader, Tom Daschle of South Dakota, said, "It is hard to imagine a plan less faithful to what seniors have been promised." Mr. Daschle added, "The more Democrats learn about this plan, the more concerned we become."
Republicans also faced questions from their own ranks. Senator Olympia J. Snowe, Republican of Maine, an architect of the bipartisan Medicare bill passed by the Senate in June, said she was "deeply concerned" about parts of the agreement, especially a provision that would require direct competition between private health plans and the traditional government-run Medicare program in a half-dozen metropolitan areas.
Still, an administration official said on Sunday that that he did not expect Senate Democrats to use their ultimate weapon, a filibuster, to block the bill.
"This legislation has got the president's support, it has bipartisan support, it has broad support among doctors, hospitals and providers," the official said. "I don't think anyone wants to kill drug coverage for seniors on a filibuster."
Congressional leaders said they could not produce a reliable vote count until lawmakers returned to the Capitol this week. But supporters of the bill suggested five reasons it should pick up votes:
The bill provides $400 billion for drug benefits in the next decade, an amount that may not be available again any time soon.
House Republicans scaled back their demands for direct competition between private health plans and traditional Medicare. The bill calls for a test of such competition, beginning in 2010.
In the final days of negotiations, House and Senate leaders agreed to provide more money to help low-income people with their drug costs.
The government would offer tens of billions of dollars to employers to encourage them to continue providing health benefits, including drug coverage, to retirees.
Medicare would provide at least $25 billion in new assistance to hospitals, doctors and other health care providers in rural areas.
House Republican leaders have recruited a team of powerful lobbyists from business trade associations, insurance companies, drug manufacturers and other industries to help them pass the legislation.
Mr. Bush's senior political adviser, Karl Rove, met with the lobbyists last week in the Capitol. The lobbyists' work is being coordinated by Susan B. Hirschmann, former chief of staff to Representative Tom DeLay, the Texas Republican who is now the House majority leader.
Among those who attended the meeting with Ms. Hirschmann were lobbyists for the United States Chamber of Commerce, the National Association of Manufacturers and drug companies like AstraZeneca and Wyeth.
Other groups supporting the bill include the American Medical Association, the American Hospital Association, the Business Roundtable and the American Association of Health Plans, which merged recently with the Health Insurance Association of America.
The A.M.A. said it would "blitz Capitol Hill with an advertising and grass roots campaign" for the bill, which would give doctors a 1.5 percent increase in Medicare fees next year, rather than the 4.5 percent cut scheduled under current law.
A major purpose of the bill is to expand the role of private health plans in Medicare. Beginning in 2006, Medicare beneficiaries could sign up for a stand-alone drug plan or could join insurance plans that cover drugs along with doctors' services and hospital care.
Some consumer groups are mobilizing opposition to the bill. Gail E. Shearer, a health policy expert at Consumers Union, said the proposed changes in the structure of Medicare were "too high a price to pay" for the new drug benefits.
Ronald F. Pollack, executive director of Families USA, a liberal-leaning consumer group, said, "This proposal does too much to destroy Medicare and too little to help seniors who can least afford their medicines."
House and Senate negotiators rejected proposals to let consumers import lower-cost prescription drugs from Canada and other countries.
The bill permits imports from Canada if the secretary of health and human services certifies that they pose "no additional risk" to public health. But that is unlikely to occur. Federal health officials have repeatedly refused to make such a certification, and drug makers strenuously oppose any move to relax current restrictions.
The bill would reduce Medicare payments for cancer drugs, based on new data suggesting that the government pays far more than the market price for such medicines.
In the House, where an earlier version of the Medicare bill passed by one vote, Republican leaders will have difficulty persuading some conservatives to vote for the legislation, which calls for a major increase in the role of government.
Representative Jeb Hensarling, Republican of Texas, said: "My guess is that most conservatives are disappointed by the agreement. The conference report has strayed pretty far from the House bill that many conservative members only reluctantly supported."
Mr. Kennedy complained that the bill favored private health plans, by paying them 10 percent more than it would cost the government to care for the same people in traditional Medicare. In addition, he said, Medicare officials would have a special fund of $12 billion that they could use to induce private plans to enter or stay in the Medicare market.
But Senator Max Baucus, a Montana Democrat who worked closely with Republicans, said the bill could be passed without Mr. Kennedy's help.
"I would never vote for a bill I thought would undermine traditional Medicare," Mr. Baucus said, "and this bill does not do that."
Mr. Baucus fought successfully to get more assistance for elderly people with low incomes.
People eligible for both Medicare and Medicaid would not have to pay more than $3 for each prescription, but this charge would increase in the future. Congress is still debating whether the co-payment should rise with consumer prices or with Medicare drug spending, which is likely to increase much faster than the Consumer Price Index.