Republican challenger Mitt Romney disclosed on Sunday that he would keep several important parts of Barack Obama's overhaul of the American health care system, altering earlier vows for a blanket repeal of the president's most significant legislative achievement.

As if to acknowledge the growing importance of the United States' aging population, health care was much on the minds of both candidates over the weekend.

Obama was drawing new attention to Romney's plans to alter Medicare, the government health insurance system for the elderly, hitting the issue hard in Florida, a swing state with a vast population of retired Americans.

Realizing his potential vulnerability on health care issues, Romney spelled out more details for the first time on what he foresees as the Republican vision.

"I say we're going to replace Obamacare. And I'm replacing it with my own plan," Romney said. "And even in Massachusetts when I was governor, our plan there deals with pre-existing conditions and with young people."

Those are two of the most popular provisions in the hard-fought Obama overhaul, and Romney adopted them in remarks aired on NBC television's "Meet the Press" Sunday morning. Obama's overhaul bans insurance companies from refusing to cover people with pre-existing medical conditions and allows young people to remain covered under their parents' plan until age 26.

"Of course there are a number of things that I like in health care reform that I'm going to put in place," he said. "One is to make sure that those with pre-existing conditions can get coverage."

Romney also moved to blunt Obama's attacks on the former Massachusetts governor's plans for further cutting taxes, saying his proposals would pay for cuts in overall tax rates by closing loopholes for high income taxpayers.

"We're not going to have high-income people pay less of the tax burden than they pay today. That's not what's going to happen," he said.

When pressed, however, Romney declined to provide an example of a loophole he would close.

Healthcare vouchers

Campaigning for a second day in the critical state, where older voters and workers approaching retirement hold sway, Obama on Sunday was expected to highlight a study by a Democratic-leaning group that concluded that on average a man or woman retiring at age 65 in 2023, would have to pay $59,500 more for health care over the length of their retirement under Romney's plan.

While Romney's changes to Medicare would affect future retirees, the study also said that Romney's plan to get rid of Obama's health care law could raise health care costs in retirement by $11,000 for the average person who is 65 years old today by reinstating limits on prescription drug coverage.

The study was conducted by David Cutler, a Harvard professor and health policy expert who served in the Clinton administration and was Obama's top health care adviser during the 2008 presidential campaign. Cutler conducted the study for the liberal Center for American Progress Action Fund.

Romney, endorsing a plan put forth by his vice-presidential running mate, U.S. Rep. Paul Ryan, wants to contain Medicare costs by giving retirees voucher-like government payments that they could use to either buy regular Medicare or private health insurance. But Cutler says older Americans would have to pay more out of pocket to cover the rising costs of health care.

Obama aides believe they successfully forced Romney to temporarily drop his emphasis on the sluggish economy last month by raising the Medicare issue in the wake of his selection of Ryan as his running mate. Romney and Ryan countered by arguing that Obama planned to cut more than $700 billion in Medicare spending over 10 years to pay for his health care plan. Former President Bill Clinton, speaking at the Democratic National Convention, said Ryan's budget plan cut Medicare spending by the same amount.

Bleak jobs report

Whether either side has gained politically from the health care debate is unclear. But Republican analysts say it did take Romney off his economic focus, which they say is essential for him to win the election, especially after a bleak jobs report that showed meagre job growth and more unemployed people choosing not to seek work. Campaigning in Kissimmee, Florida, on Saturday, Obama had already worked Medicare into his rally speeches.

"I want you to know I will never turn Medicare into a voucher," Obama told a high-energy crowd of 3,000 at the Kissimmee Civic Center. "I believe no American should ever have to spend their golden years at the mercy of insurance companies. After a lifetime of labour, you should retire with dignity and respect."

Vice-President Joe Biden, campaigning in Ohio, called the Republican plan "Vouchercare."

Biden said the Romney-Ryan plan would force "Mom" to go out into the insurance market and look for the best deal she can find. If the plan costs more than the voucher amount, "They say, 'Mom go borrow somewhere' " to pay for it, Biden said.