The Republican-controlled Senate pointed toward a showdown Sunday on a sweeping Medicare prescription drug bill that sparked a last stand by outnumbered critics and beckoned Democratic presidential hopefuls to the Capitol to join the fight.

Even so, the roster of declared Democratic supporters for the bill grew to nine, when Sens. Dianne Feinstein (search) of California and Ron Wyden of Oregon announced their intentions to vote for it. In less-than-glowing assessments, both ascribed a series of benefits and shortcomings to the bill, and Wyden said his decision was "a very, very tough call."

Sen. Edward M. Kennedy (search), D-Mass., led a filibuster against the legislation, arguing it would lead toward privatization of Medicare and warning that if they were successful, Republicans would soon be back for more. "Social Security is next. Medicare is now," he said.

Sen. Charles Grassley (search), R-Iowa, quickly disputed that, adding that opponents were playing politics and would regret it. He accused Democrats of blocking a prescription drug bill two years ago, saying they had "wanted an issue" to take into the 2002 election. "They got a defeat at the polls" instead, he said.

The measure would create a prescription drug benefit for Medicare beneficiaries for the first time since the giant health care program for seniors was created in 1965, with subsidies to help lower-income seniors pay the premiums and other costs. Additionally, it would establish a new, expanded opportunity for insurance companies to offer private coverage for seniors -- a plan viewed with favor by conservatives and with suspicion by many Democrats.

The measure cleared the House near sunup Saturday after a roll call that consumed nearly three hours rather than the allotted 15 minutes. The vote was 220-215, largely along party lines. Senate approval would send the measure to the White House, where President Bush is eager to sign it.

Senate Majority Leader Bill Frist set the first in an expected series of test votes for Monday, and officials on both sides of the issue said supporters were likely to gain the 60 votes needed to prevail.

At the same time, Senate Majority Leader Tom Daschle pledged to extend the struggle, and aides said he would join efforts to derail the legislation on other procedural grounds. In a sharply worded speech, Daschle described the bill as a windfall for drug companies. The industry "got almost everything they wanted," he said, including a prohibition on the government negotiating for lower drug prices for seniors.

The Senate's session was less a debate than a series of speeches by senators who support and oppose the bill, enlivened by the maneuvering of three Democratic presidential hopefuls to inject themselves into the clash.

Sen. John Kerry, D-Mass., who announced Saturday that he would return to Washington to join the filibuster, waited in the Capitol until his turn came to speak. "This bill is really about President Bush passing the buck on prescription drug coverage and passing the bucks from seniors to the pharmaceutical industry," he said.

Sen. John Edwards, D-N.C., flew to Washington during the day, then headed for the Senate chamber so he, too, could underscore his opposition. "We need to stand up to drug companies and HMOs and stand up for the American people," he said.

Sen. Joe Lieberman, D-Conn., announced his opposition to the bill, becoming the last of the presidential contenders in Congress to take a position. "As much as I want to give seniors a prescription drug benefit, they shouldn't have to swallow the many harmful poison pills that Republicans loaded into this bill just to get there," he said.

Two other Democratic contenders, Reps. Dennis Kucinich of Ohio and Dick Gephardt of Missouri, voted against the bill in the House.

Among the other contenders, Howard Dean and Wesley Clark both oppose the measure.

The far-reaching bill also would increase Medicare funding for doctors, hospitals and other health care providers, particularly in rural areas, where reimbursement levels are far below what is paid in other regions of the country. Additionally, the bill provides billions of dollars to companies to encourage them to retain the health coverage they provide their retirees.

For the first time, higher-earning seniors would be required to pay more for their Medicare Part B premiums than other beneficiaries. The measure also retains the current ban on the importation of lower-cost prescription drugs from Canada, and establishes tax-preferred health savings accounts for individuals with high-deductible insurance coverage.

The most contentious provision would take effect in 2010, when direct competition between traditional Medicare and the private plans starts in up to six metropolitan areas. Supporters argue that would help reduce the cost of Medicare in the long run, while opponents attack it as the leading edge of an effort by Republicans to privatize Medicare.