WASHINGTON – Americans who don't get health insurance once the system is overhauled would be fined up to $3,800 under a proposal that circulated in Congress on Tuesday as Democratic leaders cast doubt on prospects for creating a government-run insurance plan.

President Barack Obama prepared what he hoped would be a game-changing speech to a joint session of Congress on Wednesday, his top domestic priority in the balance.

After a month of contentious forums, Americans were seeking specifics from the president. So were his fellow Democrats, divided on how best to solve the problem of the nation's nearly 50 million uninsured...