LANSING, MI -- Michigan Gov. Rick Snyder is backing expansion of Medicaid under the Affordable Care Act, but critics in his own political party remain skeptical that the federal government will be able to live up to the promise of "Obamacare."

Snyder this week became the sixth Republican governor to back a Medicaid expansion that would cover adults making up to 133 percent of the federal poverty level.

The plan, according to Snyder's new budget proposal, would extend insurance coverage to approximately 320,000 individuals in the first year and eventually up to 470,000. In the process, the administration says the state could reduce its uninsured population by 46 percent and curb the number of costly emergency room visits.

The federal government would cover 100 percent of expansion costs through 2016 but gradually reduce funding to 90 percent by 2020. Federal support would save Michigan $206 million next year, according to Snyder, who proposed putting half the annual savings into a savings account designed to reduce the risk of future costs.

"I think the opportunity speaks for itself," Snyder told reporters on Thursday. "Society is paying the cost of the uncompensated care group, and we're preventing that. It's very expensive to go to the ER. The question is, can we provide better care at the individual level, improve the quality of their life and also save the government or society money by getting them out of the ER and into primary care?"

Snyder said his office studied the Medicaid issue for several months and had arrived at a decision before recent announcements from other Republican governors, including John Kasich of Ohio. But he acknowledged that fear of losing federal dollars to other states played a role in his decision-making process.

Now that he's made the decision, Snyder must sell the plan to the state legislature, where some members of his own party have repeatedly attempted to distance themselves from the faintest whiff of "Obamacare."

In November, a Republican-controlled House committee failed to advance legislation that would have allowed the state to create and manage its own health insurance exchange under the Affordable Care Act, a plan supported by Snyder. Instead, Michigan is on a path towards an exchange controlled in concert with the federal government.

The U.S. Department of Health and Human Services last month awarded Michigan a $31 million grant to plan and implement the exchange, but the state could lose that money if Republican lawmakers block its appropriation, as they did with a similar $10 million grant in 2011.

While Michigan Democrats criticized several aspects of Snyder's budget recommendations, many identified the proposed Medicaid expansion as one of the lone bright spots.

"The only reason we haven't done it yet is because Republicans have overtly politicized the Affordable Care Act so much that they will reject things that obviously help the state," Robert McCann, a spokesman for Senate Democrats, said earlier in the week. "It's not about policy, it's about politics, and that's not what people want to hear is happening in Lansing."

Republican Sen. Patrick Colbeck of Canton, speaking Thursday during an appropriations hearing on Snyder's budget, argued that the state could benefit by continuing to delay action on the health exchange, suggesting that it would leave the federal government without a way to penalize businesses with at least 50 employees who do not provide affordable health insurance, as the new law will soon require.

Colbeck also asked Snyder and Budget Director John Nixon why they were "so eager" to "get into bed" with the federal government on Medicaid expansion, which requires trust in a funding pledge made by a Congress and president who have failed to agree on a budget in several years.

"I don't know that I would use the term 'eager,'" Nixon responded. "The reality is the Affordable Care Act is happening. The reality is that everybody in Michigan on January 1, 2014, will have to have insurance. That's just a fact."

In presenting his budget to lawmakers, Snyder called Washington "a mess," suggesting that an outdated federal tax system, growing national debt and threat of sequestration cuts threaten Michigan's economic recovery.

Later, when asked whether the state should trust the federal government to make good on its Medicaid funding promise, Snyder said his call for a health savings plan is designed to mitigate risk.

"I haven't heard of any other state coming up with a concept like that, and I think it's good financial behavior to say we're just like a family, so we need money for that co-pay," he said. "…And the beauty of it is, if we don't need them for those emergencies or contingencies, then we can do our co-pay through 2034. That's a good deal."

Republican Sen. Roger Kahn of Saginaw Township, who chairs the appropriations committee, said he is not sold on Medicaid expansion because he is not sure whether the governor's plan addresses all fiscal and political risks.

For example, the Affordable Care Act provides primary care physicians with a two-year incentive to continue seeing Medicaid patients by guaranteeing them Medicare reimbursement rates. When that fixed rate expires, Kahn said, some physicians may decide to stop seeing Medicaid patients.

"An insurance card is not access," Kahn said. "It's having someone take care of you that's access. And (if a patient can't see a physician) where will these people go? To the emergency room, and then where's the savings?"

While the governor's plan does directly address the issue of physician reimbursement rates, Nixon said it's an issue that the state is monitoring and will have to deal with regardless of Medicaid expansion.

"As an administration, we didn't cut provider rates when we came in," Nixon said. "We are concerned about the access issue. It's something we are watching. It's something that we are trying to protect."

Jonathan Oosting is a Capitol reporter with MLive Media Group. Email him at joosting@mlive.com or follow at twitter.com/jonathanoosting.