SIOUX FALLS, S.D. (AP) - A new study shows that South Dakota nursing homes will lose nearly $23 a day this year on Medicaid patients, threatening long-term care in the state.

About 65 percent of patients are on Medicaid at many South Dakota nursing homes.

The federal government pays about two-thirds of the cost of the program for the poor, leaving the remaining third to states.

Only three other states lose more per patient.

In the past five years, nursing homes in Dell Rapids, Letcher and Parker have closed in part because of the Medicaid funding gap, said Mark Deak, executive director of the South Dakota Health Care Association.

"It probably isn't a question of whether there will be other closings, it's a question of when," Deak said. "They've cut into muscle, and now they're cutting into bone."

The state-federal Medicaid program, which covers health expenses for the poor, underfunds nursing homes about $4.5 billion nationally - $1 billion more than five years ago, according to BDO Seidman, a Madison, Wis.-based accounting company, which did the study for the American Health Care Association.

In South Dakota and other historically low-tax states, money for Medicaid is sparse because the state has to spread a tight budget over several programs.

At the same time, South Dakota's homes have seen a rise in assisted-living centers, which fall into the so-called retirement-home arena but cater to a broad customer base, including many seniors who are in relatively good health and in need of only minor care. As a group, they are less costly to care for, and many have money to pay for some or all of their costs. That allows many assisted living centers to charge enough to cover their costs.

However, that also leaves nursing homes with the most severely ill and costly patients, many of whom have exhausted their savings and rely on Medicaid. In South Dakota, which has one of the nation's largest elderly populations, that's helped drive the nursing-home finance problem.

Meanwhile, North Dakota, similar in size to South Dakota, had the smallest projected loss at $1.15 per patient, which officials in the North Dakota Department of Human Services attribute to the rate equalization set by the Legislature in 1990.

In North Dakota, everyone who has the same health-care needs pays the same rate, regardless of whether they pay privately or through Medicaid. Fifty-seven percent of the state's nursing home patients are on Medicaid.

Deb Bowman, secretary of the South Dakota Department of Social Services, said her staff had not yet analyzed the study, and she said she could not verify whether the problem is as significant as the report indicates.