Senate Republicans on Wednesday stood by a GOP plan to transform Medicare, one day after the party lost a conservative House district in Upstate New York amid a strong effort by Democrats to make that proposal the central issue.

The measure was defeated in the Democratic-run Senate on Wednesday.

But the unity among Republicans — with only five out of 47 voting against it — served as an important sign that party leaders remain wedded to a deficit-reduction plan that is a loyalty test for many GOP voters but is widely unpopular, according to polls.

Wednesday’s vote underscored the pressure being exerted by the party’s tea party base to stick with the plan, sponsored by House Budget Committee Chairman Paul Ryan (Wis.), and the calculation by Republican officials that they have time before the 2012 election to neutralize any of the Democrats’ political advantages. Moreover, in the Senate, the GOP has some breathing room, with only 10 members up for re­election next year and just one considered vulnerable.

Still, signs of unease about Ryan’s approach remain within the party. Several GOP presidential contenders have steered clear of the Medicare provision, with both former Minnesota governor Tim Pawlenty and former Massachusetts governor Mitt Romney, a presumed candidate, saying in recent days that they will soon release their own plans. Even some of the 40 senators who voted for it openly discussed their interest in finding alternatives.

“I don’t think there’s anybody in this room that would say it’s an article of faith,” said Sen. Bob Corker (Tenn.).

Democrats, meanwhile, celebrated their victory in New York’s 26th Congressional District as a sign that Medicare could be a winning issue in next year’s election. But some in the party have begun to acknowledge that they must engage, to at least some degree, in talks about the future of the popular entitlement, with polls showing that the public wants both parties to find solutions to the country’s fiscal ills.

Hours before the Senate vote Wednesday, former president Bill Clinton urged Congress, including his fellow Democrats, not to “tippy-toe around” Medicare, saying the program “is part of a whole health-care system that has a toxic effect on inflation.” Speaking at a conference about fiscal challenges, Clinton warned Democrats to be wary of weighing the issue solely for political gain, adding: “We’ve got to deal with these things.”

Vice President Biden, leading bipartisan negotiations to devise a plan for cutting the deficit, said Tuesday night that “big-ticket items” such as entitlements must be addressed.

The Democrats, however, are continuing to bash Ryan’s approach and are not proposing major, new ideas of their own. Policy experts said most of the ideas being circulated by the party — including government-negotiated prices for medicine that older Americans buy — reprise long-held views that Republicans oppose.

House Minority Whip Steny H. Hoyer (D-Md.) said Medicare “needs to be on the table.” But he added that he would not risk a backlash by identifying concrete changes he would support, saying, “That is the same mistake that . . . Ryan made.”

Medicare has become one of the largest contributors to the nation’s precarious financial state. The program, which provides health insurance to 47 million elderly and disabled Americans, is an enormously popular entitlement, but the part of it that pays hospital bills is forecast to run short of money within 13 years.

The Ryan plan would transform Medicare from a public insurance system that guarantees specific benefits, no matter the cost, into a program that would give beneficiaries subsidies to buy private health plans. The idea is known as “premium support,” because it would help pay for insurance premiums, and it would begin for people who turn 65 in 2022. Ryan’s version would go further than earlier premium-support proposals, because it would drop the original fee-for-service version of Medicare, dating to the mid-1960s, rather than preserving it as an alternative.

Democrats are open, for now, to a very different set of ideas, so it remains unclear whether there is space for a compromise involving Medicare changes as part of a broad plan to lessen the deficit.

According to sources on Capitol Hill and among health policy experts, Democrats remain resistant to any changes that would reduce the services Medicare covers. And at this week’s negotiating session with Biden on the deficit, there was no talk of controversial ideas that have been considered in the past: raising the eligibility age for the program or further requiring affluent older Americans to pay higher prices for the benefits. Instead, Democrats are largely looking at ideas they have advocated in the past that could affect pharmaceutical companies, medical schools and payments to doctors and other care providers .

Democrats are also quick to point out that the 2010 law designed to overhaul the nation’s health care system — legislation that House Republicans have voted to repeal — already set in motion changes that will slow Medicare spending.

One current idea, which Democrats have favored since Congress added drug benefits to Medicare in 2003, is to give the government the ability to negotiate directly with pharmaceutical companies over the prices of medicines purchased within the program. Democrats are also proposing that older Americans who are poor enough to qualify for Medicaid as well as Medicare, be able to get medicine at the lower prices available through Medicaid — an idea that was considered, but ultimately not included, in last year’s health care law.

In addition, Democrats are considering changes to Medicare’s subsidies for graduate medical education and exploring ways to clamp down further on fraud and abuse in the program.

In an early sign of the likely resistance to even these more modest Democratic ideas, a coalition of hospital organizations announced Wednesday that it was beginning to run advertisements in Washington-area publications protesting cuts, beyond those in last year’s health care law, as part of a deficit-lowering plan. “Enough is enough,” the ad says.

The budget plan passed the House with all GOP votes on April 15. The proposal was one of several budget measures the Senate voted on Wednesday. Senate Majority Leader Harry M. Reid (D-Nev.) pushed to hold them that day, less than 24 hours after the New York polls closed, and allowed several competing visions to be offered. Each was doomed to defeat. But that was part of the point: Both parties wanted to prove that the other’s opening proposal could not secure the bipartisan collection of 60 votes needed to win final passage in the Senate.

Every Democrat opposed the Ryan proposal over the Medicare issue, as did four centrist Republicans — Sens. Scott Brown (Mass.), Susan Collins (Maine), Olympia J. Snowe (Maine) and Lisa Murkowski (Alaska). Brown could be vulnerable in his re­election bid next year. Snowe, while facing a possible tea party challenge in the Republican primary, cast a vote that could help her in the general election.

Sen. Rand Paul (Ky.), the fifth Republican defector, said the Ryan plan was too timid in dealing with the $14.3 trillion national debt.

Minority Leader Mitch McConnell (R-Ky.) then called up Obama’s initial 2012 budget proposal for consideration. Both parties had criticized the plan, saying it would offer only a minor reduction in the national debt. The president has since put forward a new blueprint that would shave $4 trillion from projected deficits over 12 years. With Obama himself abandoning his initial budget proposal, not a single senator voted for it.

Even as some Republican strategists acknowledged that Medicare had played a role in the New York defeat, they said they intend to double down on their sales pitch.

Grover Norquist, president of the conservative Americans for Tax Reform, said his group plans to distribute to 150,000 activists nationwide five-minute videos of Ryan describing his proposal. Norquist said he is also exploring a campaign training seminar to teach grass-roots operatives how to better defend what he calls the doctrine of the modern-day GOP.

“The best defense is clarity,” Norquist said. “The challenge will be to teach each of our activists to deliver the Ryan speech.”

Policy experts say Democrats will remain eager to let the GOP pursue its course.

“I just don’t see the Democrats willing to take Ryan and the Republicans off the limb they are dangling from,” said Robert Laszewski, a health policy specialist with clients across the health-care industry. “Democrats are just licking their chops on this one.”