IN the debate over health care reform, one issue looms large: whether to have a public option. Should all Americans have the opportunity to sign up for government-run health insurance?

President Obama has made his own preferences clear. In a letter to Senators Edward M. Kennedy of Massachusetts and Max Baucus of Montana, the chairmen of two key Senate committees, he wrote: “I strongly believe that Americans should have the choice of a public health insurance option operating alongside private plans. This will give them a better range of choices, make the health care market more competitive, and keep insurance companies honest.”

Even if one accepts the president’s broader goals of wider access to health care and cost containment, his economic logic regarding the public option is hard to follow. Consumer choice and honest competition are indeed the foundation of a successful market system, but they are usually achieved without a public provider. We don’t need government-run grocery stores or government-run gas stations to ensure that Americans can buy food and fuel at reasonable prices.

An important question about any public provider of health insurance is whether it would have access to taxpayer funds. If not, the public plan would have to stand on its own financially, as private plans do, covering all expenses with premiums from those who signed up for it.