Under Ryan's plan, for anyone younger than 55 the basic Medicare program for medical and hospital care would be replaced by a system in which insurance companies would offer coverage while the government contributed toward the cost of premiums. The program would remain unchanged for anyone 55 or older, including millions who currently receive benefits.

Kathy Hochul's victory over Republican Jane Corwin in a multi-candidate race was the best political news in months for Democrats, who were voted out of power in the House and lost seats in the Senate last year in what President Barack Obama memorably dubbed a shellacking. She gained 47 percent of the vote, to 43 percent for her rival and 9 percent for Jack Davis, a former Democrat who ran as a tea party contender.

At the same time, Democrats stressed they did not view the race as a reason to walk away from high-profile bipartisan deficit-reduction talks being led by Vice President Joe Biden.

For Republicans, the New York race provided fresh evidence of turbulence for a Medicare remake they tout as a long-term answer to the program's financing. In the weeks since they unveiled it, the proposal has been less than enthusiastically received by the public, judging from polls.

GOP presidential hopeful Newt Gingrich criticized it, and while he later apologized to Ryan he has not recanted his opposition. A second contender, former Minnesota Gov. Tim Pawlenty, said during the day he will have an alternative that differs in unspecified areas from the one in the party's budget in the House.

Israel and other Democrats said Hochul's victory showed that the Medicare-overhaul proposal would prove a political dead weight for Republicans in dozens of races in the 2012 congressional elections.

It also is likely to embolden liberals who are not generally supportive of deficit cuts now under negotiation on the order of trillions of dollars.

Yet public opinion polls show strong support for reining in deficits, particularly among independent voters. And Obama, readying for his own re-election campaign, has dispatched Biden and other top officials to negotiations aimed at reaching a compromise with Republicans.

"Budget talks are proceeding in good faith and will continue," said Nadeam Elshami, a spokesman for House Democratic leader Nancy Pelosi.

The party's second-in-command in the House, Rep. Steny Hoyer of Maryland, has said repeatedly that changes to Medicare should be on the table as part of deficit reduction talks, although he and others in his party remain implacably opposed to the Republicans proposal.

In an interview, Israel said Democrats would work with Republicans to strengthen Medicare "but not to do away with it."

Republicans want "to end Medicare as we know it," the president told an audience of invited guests last month, Ryan and other GOP lawmakers among them.

Democratic strategists have privately urged the party's leaders to criticize the overhaul plan, in part to try and regain the allegiance of older and independent voters who helped Republicans in the 2010 elections.

Sen. Patty Murray of Washington, chair of the Senate Democratic campaign organization, said she, too, intended to make use of the issue in the fall.

"I'm confident that Senate Democrats will be able to play offense in races across the country by remaining focused on the Republican effort to end Medicare in order to" cut taxes for the wealthiest Americans and big corporations, she said.

In the race in New York, Hochul injected the GOP Medicare plan into the campaign weeks ago. Running in a conservative district, she aired ads saying she wanted to reduce government spending while accusing Corwin of favoring Medicare cuts to pay for tax cuts for the wealthy.

Corwin quickly counterattacked, accusing Hochul of wanting to cut Social Security as well as Medicare.

Both the Democratic campaign committee and the House Majority PAC, an outside group aligned with the Democrats, also aired ads critical of the GOP Medicare plan.

But the National Republican Congressional Committee did not mention the issue in running as much as $400,000 worth of television advertising in the district around Buffalo and Rochester. Instead, the group ran a commercial linking Hochul to Pelosi, an echo of the type of ad that proved effective in the 2010 campaigns.

Paul Lindsay, a spokesman, declined to say whether the organization wished it had acted differently. But in the future, he said, "Republicans will take this result as a call to action to challenge Democrats at every turn on their irresponsible plan to bankrupt Medicare."

American Crossroads, an organization aligned with Republicans, spent more than $600,000 on television ads without seeking to counter the Democratic attacks.

Jonathan Collegio, a spokesman, said polling showed Medicare was the largest policy issue in the campaign "by a superslim and superlow plurality of 21 percent."

He said one out of five voters said it was the most important issue, yet five out of ten voted for Hochul. "When you look at it that way, it's really not the big deal that everyone made it out to be."

Hochul will be sworn in within days, the first Democrat to represent the district in four decades. She replaces Chris Lee, who resigned after shirtless photos he sent to a woman he'd flirted with on Craigslist surfaced online.