The health insurance companies claim that the world will end if Congress includes a government option in the comprehensive health reform bill. We do not share the insurers' apocalyptic vision, and judging by the polls, neither do the American people.

What might end is the insurance companies' ability to game the system in the name of unlimited profits. That's their real fear.

It is to check those profits and other costs, by way of competition, that President Obama wants to include a public plan as an option alongside private plans. He says a public option would give Americans "a better range of choices, make the health care market more competitive, and keep insurance companies honest."

The American people agree. Two polls this month found that about 75 percent support a public option.

The insurance industry has attacked the public option for its unintended consequences. It says that "a government plan -- no matter how it is initially structured -- would dismantle employer-based coverage, significantly increase costs for those who remain in private coverage, and add additional liabilities to the federal budget."

One problem with the whole debate, though, is that no one knows in any detail how a public plan would be structured, so it is difficult to predict its consequences. A study by the Lewin Group shows that the details will make all the difference.

If, for example, the public plan used Medicare payment levels to providers, premiums would be up to 30 percent less than those for comparable private plans. If, as the president proposed during his campaign, eligibility were limited to small employers, individuals and the self-employed, enrollment would reach 43 million people, and about 32 million people would drop private coverage, according to the study. However, if the reimbursement rates used by private insurers were used by the public plan, only 10 million people would switch from private plans.

If the public plan were opened to all employers, at Medicare reimbursement rates, the results would be enormous. An estimated 131 million people would enroll, decimating private insurance. But Obama has said he wants a plan that would allow people to keep their current employer-provided insurance if they choose.

Congress must not allow the insurance industry to stampede it away from a public option -- something the public wants -- before the specifics and its consequences are even debated.