WASHINGTON – The House-approved Republican budget plan would eventually raise the age at which seniors are eligible for Medicare coverage, according to the nonpartisan Congressional Budget Office.

Currently at 65, the plan would increase the Medicare eligibility age by two months per year starting in 2022, until it hits 67 in 2033, the scorekeeper concluded in its analysis (pdf). The little-noticed feature of the controversial blueprint was brought to light Tuesday by Jon Cohn of The New Republic.

"Raising the age at which Americans become eligible for Medicare, or whatever program Republicans put in its place, would make health insurance more expensive for businesses, workers, and their employees, all while leaving one-fifth of future 65- and 66-year-olds with too little insurance or none at all," concluded Cohn, an author and expert on health care policy.

Liberal columnist Paul Krugman piled on the criticism in his New York Times blog, pointing out that the change would disproportionately harm low-income Americans who are most in need of health care assistance, and for whom life expectancy has risen at a slower rate.

The GOP proposal, drafted by House Budget Committee Chairman Paul Ryan (R-WI), would privatize Medicare and turn it into a voucher program in the long-run. It would remain intact for the next ten years, but Americans turning 65 after 2021 would not be allowed to enroll in the single-payer program, and would instead be given subsidies to buy private insurance.

The value of the subsidies -- dubbed "premium support payments" -- would likely grow at a slower rate than medical cost inflation. The CBO projects that, by 2030, the average 65-year-old would pay 68 percent of his or her health care costs out of pocket, as compared to 25 to 30 percent under current law.

A spokesman for Ryan did not immediately return a request for comment.

The plan passed the House by a vote of 235-193. All but four Republicans -- and no Democrats -- voted for it. Senate Democrats have decreed it a nonstarter, and President Barack Obama has rejected it.

House GOP lawmakers who supported it have faced constituent anger back home in recent days, and Democrats are determined to hang it around the party's neck in the 2012 elections.