ATLANTA  In the two weeks since the Senate majority leader, Harry Reid, embraced a proposal that would allow states to opt out of a new government health insurance plan, state leaders have begun debating whether to take part, and the question has emerged as a litmus test in some campaigns for governor.

The proposal, which is being woven into the Senate health care bill, would shift some power to the states and would foist upon state leaders the burden of a choice that, in some cases, could pit principle and politics against pragmatism. States would be given the right to opt out of only the public plan, not from the tax increases needed to subsidize coverage for the uninsured.

The bill that passed the House on Saturday night includes a nationwide public plan without an opt-out provision, a difference that would be settled by a conference committee.

Several state officials said that if Mr. Reid’s proposal carries the day, many governors are likely to accept the new plan rather than incite an ideological battle mirroring the fight in Congress.