WASHINGTON -- Republicans are taking a bold political gamble by pushing historic changes in Medicare and Social Security.

The popular programs, designed primarily to provide health care coverage and income security for seniors, have been politically untouchable for decades.

But presumptive GOP presidential nominee Mitt Romney, as well as most congressional Republicans, embrace sweeping changes that, among other things, would alter dramatically how seniors get health coverage a decade from now.

Democrats think the GOP has given them a gift, an issue they can use to illustrate how Republicans and their well-heeled friends are ready to abandon generations-old societal obligations to seniors.

But it’s not clear who’s got the political advantage, if any. The major GOP Medicare plans wouldn’t affect anyone now 55 and over, and those under that age may care more about arresting the ballooning federal debt – and Medicare’s impact on it – than the health of the program decades from now.

Study after study has found that to pare the government’s record debt significantly, the ever-rising costs of Social Security and Medicare must be slowed. Social Security and Medicare accounted for 36 percent of federal spending in fiscal 2011, and as baby boomers age, those costs are projected to keep rising.

Polls show that the economy is the primary voter concern in the 2012 elections, but these two giant entitlement programs are part of the economic equation.

“There is one big issue, and that’s the economy,” said Peter Brown, assistant director of the Quinnipiac University poll. “For some people there are aspects of it more important than others, but generally the economy is issue one through 29.”

A Pew Research Center poll in January found that securing Social Security ranked fifth and securing Medicare seventh on the public’s priority list for Congress; strengthening the economy was first, followed by improving the job situation, combating terrorism and reducing the budget deficit. Improving education ranked sixth.

Still, even suggesting tinkering with Medicare and Social Security carries political risks . The eligibility age for full benefits is now gradually increasing. For those born after 1960, it will be 67. Romney would increase it further, allowing it to rise along with increases in longevity. He also would slow the growth in benefits somewhat for wealthier recipients; no details have been disclosed.

“Romney’s playing with fire. You always are when you delve into Social Security and Medicare,” said Larry Sabato, director of the Center for Politics at the University of Virginia.

Yet this could be the year the conventional political rules change, because the skyrocketing federal debt is such an ominous threat to the nation’s economic well-being.

“It’s hard to ignore that piece (the debt) totally,” Sabato acknowledged.

The GOP plan, proposed in several similar formats, works generally like this: After 2022, seniors newly eligible for Medicare would get federal subsidies to buy insurance coverage. They could purchase that coverage from Medicare, but they would have the option of buying a policy from a private company.

All insurance plans would have to offer coverage “at least comparable to what Medicare provides today.” If seniors wanted a more expensive plan, they would have to pay the difference between the federal aid and the premiums’ price. No one currently 55 or older would be affected.