WASHINGTON — The rolls of America’s oldest old are surging: Nearly 2 million now are 90 or over, nearly triple their numbers of just three decades ago.

It’s not all good news. They’re more likely than the merely elderly to live in poverty and to have disabilities, creating a new challenge to already strained retiree income and health care programs.

First-ever census data on the 90-plus population highlight America’s ever-increasing life spans, which are redefining what it means to be old.

Joined by graying baby boomers, the oldest old are projected to increase from 1.9 million to 8.7 million by mid-century — making up 2 percent of the total U.S. population and one in 10 older Americans. That’s a big change from more than a century ago, when fewer than 100,000 people reached 90.

Demographers attribute the increases mostly to better nutrition and advances in medical care. Still, the longer life spans present additional risks for disabilities and chronic conditions such as arthritis, diabetes and Alzheimer’s disease.

“If I get stuck with something I can’t handle, I yell for the kids,” says Betty Mae Gutoski, 85, of Muskegon, Mich., who says she expects to live past 90. The colon cancer survivor lives alone and says she is “comfortable,” getting occasional help with yard work from her son and grandson, who live next door.

Gutoski said in a telephone interview that she maintains her health by leading a busy life — driving, grocery shopping once a week, sewing, visiting the senior center, volunteering and meeting her friends for lunch — but she acknowledges having some fears. “My big worry is becoming a burden on my family,” she said.

Richard Suzman, director of behavioral and social research at the National Institute on Aging, which commissioned the report, said cases like Gutoski’s are increasingly common.

An Associated Press-LifeGoesStrong.com poll in June found that more than one in four adults expect to live to at least 90, including nearly half of those currently 65 or older.

“A key issue for this population will be whether disability rates can be reduced,” Suzman said. “We’ve seen to some extent that disabilities can be reduced with lifestyle improvements, diet and exercise. But it becomes more important to find ways to delay, prevent or treat conditions such as Alzheimer’s disease.”

According to the report, the share of people 90-94 who report having some kind of impairment such as inability to do errands, visit a doctor’s office, climb stairs or bathe is 13 percentage points higher than those 85-89 — 82 percent versus 69 percent.

Among those 95 and older, the disability rate climbs to 91 percent.

On Thursday, the Census Bureau said it was putting out its study of the 90-plus age group at NIA’s request in recognition of longer life expectancies, which are just over 78 for babies now being born.

By the time a person reaches 65, Americans are generally expected to live close to 20 years longer, up from 12 years in 1930. At age 90, their expectancy is another five years.

“Given its rapid growth, the 90-and-older population merits a closer look,” said Wan He, a Census Bureau demographer who wrote the report. “The older people get, the more resources they consume because of health care, and disability rates significantly increase. This creates demands for daily care, and for families, the care burden increases dramatically.”

The findings come as a special congressional committee struggles to meet a Nov. 23 deadline to cut more than $1 trillion from the federal deficit over 10 years. Major sticking points are proposals to increase tax revenue as well as trim Social Security and Medicare spending, such as by increasing the Medicare eligibility age.

“As we look at these numbers, we see just how critically important programs like Medicare, Medicaid and Social Security are, especially for the very old in America,” said David Certner, legislative policy director at AARP. “These are the people — mostly single elderly women — who can least afford a cut to their Social Security cost-of-living adjustment.”

“Many more also will come to rely on Medicaid as the largest payer of long-term services and supports in our country,” he said.