AUGUSTA — A bill to expand Medicaid eligibility to more low-income Mainers won initial support in the Republican-controlled Senate by a single vote Tuesday.

The measure is likely to pass in the Democratic-controlled House, but faces an all-but-guaranteed veto from Gov. Paul LePage, who has rebuffed past attempts to expand Medicaid under the federal Affordable Care Act.

The Maine Senate voted 18-17 to advance the bill, L.D. 633, after senators spent about an hour debating whether expansion would help or hurt the state’s finances. Thirty-one other states – including the five other New England states – have expanded Medicaid since President Obama’s health care law took effect, but not all in the same fashion.

The bill – sponsored by two moderate Republican senators, Tom Saviello of Wilton and Roger Katz of Augusta – would use the Affordable Care Act’s marketplace to expand Medicaid but require beneficiaries to pay small premiums for their insurance. Such a “private option” model has been adopted in several states where Republicans and Democrats share control of the government.

“If we have an opportunity to provide coverage to over 70,000 of the neediest Mainers in a financially responsible way, we should do it,” said Sen. James Dill, D-Old Town.

All 15 Senate Democrats plus three Republicans – Saviello, Katz and Sen. David Woodsome of North Waterboro – voted in favor of the bill.

The bill would authorize the state to accept federal Medicaid funds to provide health insurance to people earning between 100 percent and 138 percent of the federal poverty level. The federal government would pay 100 percent of the expansion costs through 2016, with the federal share declining to 90 percent by 2020.

Republicans who voted against the measure warned that the federal government shouldn’t be trusted to live up to those funding promises, especially considering that a future president could change the rules. They also pointed out that other states that have expanded Medicaid have underestimated their costs despite the windfall of federal funds from an expansion.

Sen. Eric Brakey, R-Auburn, who co-chairs the Legislature’s Health and Human Services Committee, said expansion “would not only be incredibly expensive in the short term … but disastrous in the long run.”

“Should be we bet our future on the financial solvency of the federal government that only knows how to run up the credit cards?” Brakey said in a floor speech. “When the federal government hits the inevitable brick wall at the end of this unsustainable road, who will be left holding the bag on Medicaid expansion?”

There have been conflicting estimates for how much expansion would save or cost Maine.

In its fiscal note on the bill, the Legislature’s nonpartisan Office of Fiscal and Program Review estimated the state would spend $93 million in General Fund revenue on expansion through fiscal year 2018-19 but receive nearly $1.2 billion in federal funds during that period. The Maine Department of Health and Human Services, meanwhile, estimated that expansion would cost the state $315 million over the next five years.

Responding to Brakey’s account of costs borne by other states, Saviello pointed out that none of the 31 states has reversed a decision to expand Medicaid.

“There is concern that, in fact, a new president will change the plan,” Saviello said. “Well, I can’t imagine those 31 states – with senators from every one of those states that have expanded – being told, ‘I’m sorry, we’re cutting you off.’ “

This is the sixth attempt to expand Medicaid in Maine under the Affordable Care Act in recent years. All previous attempts have fallen to Republican opposition in the Legislature or to LePage’s vetoes.

This year, supporters have sought to try to tie the expansion to Maine’s opiate epidemic, pointing out that expansion would help more addicts access the treatment they need for recovery.

Sen. Anne Haskell, D-Portland, also pointed out that the list of organizations supporting expansion includes the Maine Police Chiefs Association, the Maine Medical Association, the Maine Hospital Association and the Maine Sheriffs’ Association.

The bill now goes to the House, where Democrats hold the majority of seats. But the one-vote margin in the Senate falls well short of the two-thirds majority needed to override a LePage veto.