The Obama administration hopes to give all Americans the option of buying into a public, Medicare-style health insurance plan. That is now shaping up to be the biggest flash point in the emerging debate about healthcare reform. Advocates of a Medicare-style plan say it would give consumers a lower-cost alternative to private insurance, forcing those private insurers to become more responsive to consumer needs. Opponents counter that it would undermine the private health insurance market by prompting millions of businesses to switch to the cheaper, public alternative. In the long term, they argue, that would undermine consumer choice in healthcare. Lawmakers and their staffs are currently hammering out the details of reform legislation that is expected to go to the floor in June. But interest groups on the right and left have already begun a fierce ideological battle, with each side trying to shape the public’s perception of a public insurance plan.