WASHINGTON -- Appealing to tea party voters as he seeks to regain his front-runner status in the Republican presidential race, Mitt Romney outlined plans Friday for deep federal spending cuts and dramatic changes to popular entitlement programs such as Social Security and Medicare that immediately drew fire from Democrats.

Before a polite audience that gathered for the Americans for Prosperity summit in Washington, Romney said he hoped to cut $500 billion from the federal budget by 2016, a goal intended to pare back federal spending from 24 percent to 20 percent of the nation's gross domestic product.

To reach that target, Romney's campaign said he would save $100 billion by capping Medicaid spending for the poor and giving control of that program to the states. He also called for raising the eligibility age for Social Security benefits and cutting the level of nonsecurity discretionary spending to pre-2008 levels.

Perhaps the most controversial changes were in the Medicare program (though the campaign said they would not affect current seniors or anyone nearing retirement).

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Borrowing some elements from Rep. Paul D. Ryan, R-Wis., Romney's plan calls for transforming Medicare to a "premium support system" that would give seniors a set amount of money that they could use to purchase a health care plan. In a move the campaign said would encourage competition and lower the program's cost, Medicare would be one of many plans available in the marketplace. All of the plans would have to offer a level of coverage comparable to what Medicare provides today, Romney aides said.

"The future of Medicare should be marked by competition, choice and by innovation -- rather than bureaucracy, stagnation and bankruptcy," Romney said in his speech. "Our path for the future of Social Security and Medicare is honesty and security."

The Democratic Party branded the proposal as one "only a billionaire could love," while President Barack Obama's presidential campaign said the spending reductions would "devastate key middle-class programs."