CONCORD, N.H. — The New Hampshire Senate on Thursday approved using federal Medicaid money to buy private health insurance for thousands of poor adults, with supporters emphasizing the benefits to the state’s economy and the health of its residents and opponents arguing taxpayers would be stuck with the bill when federal money drops off.

The Republican-controlled Senate voted 18-5 in favor of the bipartisan plan, which has a good chance of passing in the Democratic-controlled House by early April.

New Hampshire is one of six states that have not decided whether to expand Medicaid under the federal health care overhaul law. Under the Senate bill, it would create a 2 1/2-year pilot program using 100 percent federal funding to expand health care coverage. Anyone under 65 who earns up to 138 percent of federal poverty guidelines – about $15,856 a year for a single adult – could qualify.

The state estimates 12,000 adults could begin receiving coverage in as little as a month under an existing program to subsidize employer-based coverage while 38,000 others would receive coverage through the state’s Medicaid managed care program starting this summer. The adults on managed care would be moved onto private insurance in 2016 if a federal waiver is approved by March 31, 2015. If the waiver is denied, their coverage would be phased out over three months.

Under the plan, the expansion would end if federal funding drops below 100 percent and would end regardless at the end of 2016 if the Legislature doesn’t reauthorize it. Critics argued that once taxpayer subsidized coverage is provided, lawmakers will lack the courage to end it.

“This bill is going to cost the people of New Hampshire – when the federal government stops paying for it and when the Legislature doesn’t have the conviction to stop it – $400-$800 million,” said Sen. Andy Sanborn, R-Bedford.

Sanborn said taxpayers struggling to pay their own insurance premiums shouldn’t face higher taxes to provide better coverage for others.

“We’re telling the taxpayers of New Hampshire that we’re going to charge them with buying other people’s mansions while they have to live in tents,” said Sanborn, who also questioned whether the federal government will live up to its funding promise.

Sen. Jim Rausch, R-Derry, took exception to that argument. “I just lost a dear, close friend yesterday – under 50 years of age. There is no guarantee. I don’t know what tomorrow brings, but what this bill brings is 100 percent paid for by the federal government,” he said. “It does protect the taxpayer. I’m getting a little tired of hearing about what might happen in the future, because I don’t know what’s going to happen tomorrow.”

Other supporters argued that the bill will improve the health of currently uninsured residents by providing access to affordable preventive and primary care. That would reduce the amount of uncompensated care provided by hospitals, which could help drive down premium costs and help struggling businesses, they said.

“When I go and talk to business leaders, they tell me the largest problems they face are, Number 1, the high cost of health care, Number 2, the high cost of health care and Number 3, the high cost of health care,” said Sen. Jeb Bradley, R-Wolfeboro. “This hidden tax is larger than any other tax we have in New Hampshire, and who’s paying it? We’re all paying it, and business leaders are crying out for help.”