Is the public option going to be Medicare?

[BattyDem]

What I mean is, would they be expanding Medicare by allowing people under 65 to choose it has their health care plan, or would it be a new, as yet unnamed plan?

The reason why I'm asking ...
I heard that the current bill does not require participation by doctors, hospitals, etc. Of course, if the public option was simply an expansion of Medicare, then presumably, providers who currently accept Medicare would continue to do so. However, if the public option is a new plan, what would prevent all of the insurance companies from saying, "If you accept the public option, you cannot participate in our plan." Obviously, no provider would want to have the public option plan as their only source of patients and income, so that would pretty much kill the plan before it even gets off the ground.

I don't know all the "ins and outs" of the insurance game, so if I'm totally wrong (and I hope I am), please enlighten me. :-)

On edit: I know the public option isn't even a done deal, yet ... I'm just being optimistic and trying to think ahead. :-)