Phoenix ? Republicans in more than a dozen states opposed to President Barack Obama’s push for health care overhaul have mounted state-driven efforts to block federal intervention in health care, with some early success.

The push-back centers in some areas on fact — Obama’s stated determination that all Americans should be required to get health care coverage, for example. Other resistance, though, is based on unfounded notions of what has been proposed — fears, for example, that the nation would adopt a single-payer system in which the government would take over health care, something Obama specifically disavowed on Wednesday.

Even if state lawmakers succeed, doubts remain over whether their proposals would take effect if a federal overhaul were passed. Experts say federal law likely would trump such state changes.

“My sense is that if they pass a comprehensive reform bill, it would probably pre-empt what the state is doing,” said Paul Bender, a professor at Arizona State University’s law school and an expert in constitutional law.

Lawmakers in eight states, only half of which are controlled entirely by Republicans, have filed proposals this year to ask voters to amend state constitutions to prohibit what they bill as restrictions on a person’s freedom to choose a private health care plan, mandatory participation in any given plan and penalties for declining coverage. Similar measures were considered in two other states, though they wouldn’t have been decided by voters. And lawmakers in three other states say they plan to file similar ballot proposals in the coming months.

As far as ballot initiatives, Arizona is the only state so far to put the proposal on the 2010 ballot.

Health care proposals in other states have had less traction. A measure was voted down in the Republican-controlled legislatures in North Dakota and Wyoming, and no action has yet been taken on measures in Michigan and Minnesota. The proposal never made it out of its first committee before the Democratic-controlled New Mexico Legislature ended its last session.

A version of it was introduced in Ohio last month, and Florida lawmakers will consider it when they reconvene next spring.

Similar proposals were filed in two other states, neither of which gave voters the last word. Indiana’s Senate forwarded to Washington a nonbinding message urging protections of individual health care freedoms. A binding proposal in West Virginia didn’t clear its statehouse before its session concluded.

Lawmakers in Kansas, Louisiana and Georgia said they plan to file similar ballot proposals in the future.