BOSTON -- President Barack Obama and his congressional allies have made insuring nearly all Americans a major goal of overhauling the nation's health-care system. One of their toughest challenges will be trying to cover people like Ron Norton of Worcester, Mass.

Mr. Norton, 49 years old, is an adjunct professor at a local community college who earns about $40,000 a year. He's also one of roughly 200,000 Massachusetts residents who remain uninsured despite a state law requiring residents to have health insurance.

"I can't use up all of my savings just to buy mandatory insurance," Mr. Norton says. It's like penalizing "the homeless for refusing to buy a mansion."

As lawmakers hammer out legislation aiming to extend coverage to the country's 46 million uninsured, one of the most sweeping proposals has so far stoked relatively little debate: a requirement that nearly all Americans carry health insurance, much like drivers are required to have car insurance.

All of the major health bills winding through Congress feature a so-called individual mandate similar to the one in Massachusetts. Mr. Obama supported the idea in his speech to Congress last week. Such a mandate, proponents argue, is necessary to keep premiums affordable: The healthy, who are relatively cheap to cover, help pay for the sick.