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GOP vice presidential candidate Paul Ryan told hundreds of seniors how he and Mitt Romney, if elected, would protect Medicare, while President Obama argued their plan would only increase participants' cost – as both camps Saturday traded jabs on the hot campaign topic of Medicare in the battle to win over seniors by November.

Ryan made his pitch at The Villages, a sprawling retirement community in central Florida, where he walked on stage with mother Betty Douglas Ryan, a Medicare recipient.

"Our solution to preserve, protect and save Medicare does not affect your benefits,” Ryan told the crowd. “It’s a promise that must be kept. But in order to make sure we can guarantee that promise … we must reform it for my generation.”

The Wisconsin congressman and House Budget Committee chairman said Medicare will remain unchanged for those 55 and older and proposed a plan that would give future participants the option to use a private insurer.

He also went on a direct attack against President Obama's Medicare plan, arguing the president took $716 billion from the program for startup funds for his health-care reform law.

"Medicare will not be used as a piggy bank for ObamaCare," Ryan said.

Within minutes the Obama re-election campaign said Ryan has failed to "tell the truth" about the Republican plan, which was followed by the president arguing his opponents' plan would increase a senior's cost by $6,400 annually and most benefit the wealthy.

"Their plan makes seniors pay more so they can give another tax cut to millionaires and billionaires," Obama told an estimated 2,000 people at the Windham High School, in Windham, N.H.

Obama also argued he has already reduced Medicare fraud and saved seniors hundreds of dollars annually on prescription drug costs. He repeated that message at a later stop in Rochester, N.H..

Ryan said the Romney campaign's plan has bipartisan support in Congress and is rooted in a 1990s, Clinton-area program.

Ryan's mother lives part-time in the Ft. Lauderdale, Fla., area.

"She planned her retirement around this promise" of Medicare, Ryan said. "That's a promise we have to keep."

Obama campaign spokesman Danny Kanner said Romney and Ryan know a detailed debate about their Medicare voucher plan is "politically suicidal so they're not telling the truth about its impact on current seniors."

The Romney campaign went on the attack even before Obama’s first speech.

"Three years ago, President Obama promised New Hampshire seniors that ObamaCare wouldn't impact their Medicare benefits – but that’s exactly what it did," Ryan Williams, campaign spokesman said.

According to the nonpartisan Congressional Budget Office, Medicare over time would spend thousands less per senior under the Ryan plan than under current policy. Critics say that would shift heavy costs to individual retirees. The government could always spend more than anticipated to meet changing realities, but at the cost of deeper deficits.

Ryan, in his roughly 15-minute speech, also praised Romney's leadership and vowed that he and the GOP presidential candidate will improve the U.S. economy, with an unemployment rate about 8 percents for more than three years.

"He is a leader who will make tough decisions to get Americans back to work," Ryan said. "We will lead."

The Associated Press contributed to this report.