The combination of an aging population and a weak economy is putting a strain on the finances of Social Security and Medicare.

New projections by trustees who oversee the benefit programs reveal both will be unable to pay bills in future years unless Congress acts.

Medicare is in worse shape than Social Security because of rising health care costs.

"I don't know how to make it clear to the public, but in my mind the sirens are going off," Mary Johnson, policy analyst for the Senior Citizens League, said. "I wouldn't say we're under attack, but we are in a very, very serious position."

Last year, the trustees projected the Medicare hospital insurance fund for seniors would run out of money in 2024. Social Security's retirement fund was projected to be gone by 2038, and the disability fund drained by 2018.

More than 56 million people -- including retirees, disabled workers, spouses and children -- receive Social Security. About 50 million older Americans are covered by Medicare.