If health reform includes a public health insurance plan whose payments mirrored Medicare payment levels, premiums for comparable private insurance would cost 30% more and siphon off about 32 million people who have private coverage, a new study suggests.

Since most of the proposed health care reform proposals being discussed by Congress and President Barack Obama involve a public-private partnership, the Lewin Group, a health care consulting firm, explored possible effects of a public health plan when competing for enrollment with the private insurance companies.

If payments followed the Medicare model, then on average, the monthly premium in the public plan for a typical benefits package would be $761 per family, compared with an average of $970 per family in the private market for the same coverage, the Lewin Group analysis projects.

If eligibility is limited to only small employers, individuals and the self-employed, as proposed by Obama, then public plan enrollment would reach 42.9 million people. The number of people with private coverage would fall by 32 million people in that scenario, the report suggests. If private payer reimbursement levels are used by the public plan, enrollment would be lower, with only 10.4 million people switching to the public plan from private insurance, according to the report.

About 170 million people are enrolled in private health insurance in the U.S. Another 45.5 million people lacked any health coverage last year, according to government figures, and within that total of uninsured people were roughly 11 million people who had access, but opted out of coverage.

If the public plan is opened to all employers at Medicare payment levels – a proposal advanced by former Sen. Hillary Clinton and Sen. John Edwards while campaigning last year -then about 131.2 million people are likely to enroll in the public plan. Under this scenario, the number of people with private health insurance would decline by 119.1 million people, effectively shifting two-thirds of people with private coverage to a public program. If the higher private-payer levels are used, enrollment in private insurance would decline by only 12.5 million people, Lewin Group estimates.