The nation’s largest senior citizens group questioned whether Medicare provides good enough coverage Wednesday, saying that elderly Americans spend almost a fifth of their incomes on health care.

“The challenge for reforming Medicare in the future is not just going to be trimming there and here to keep costs down, but also taking a look at the adequacy of the program for people it’s supposed to protect,” said John Rother, a spokesman for the American Association of Retired Persons.

Medicare, the nation’s health insurance program for the elderly, is open to all Americans over age 65. It provides wide-ranging coverage and paid benefits of $5,032 a person on average last year, AARP said.

But in 1997, Medicare participants still shelled out an average 19 percent of their incomes, or $2,149, for health care, the study found.

For people on Medicare living below the federal poverty level - about 3.5 million senior citizens - out-of-pocket health care costs ate up 35 percent of income, AARP said, and only about 40 percent of low-income elderly people got help from state-run Medicaid programs for the poor.

“I think the figures really are alarming,” said Rother. “Most poor seniors are not protected.”

Out-of-pocket costs to Medicare beneficiaries include a $43.80-a-month premium, $100 annual deductible and 20 percent co-payments for non-hospital care and a $760 deductible for hospitalization plus co-payments after the 60th day.

Medicare does not cover many expensive services and products, including routine physicals, prescription drugs, glasses and most dental care. Most senior citizens buy private supplemental insurance, known as Medigap, to help pay these bills. AARP included the cost of Medigap premiums in its calculations.