The Massachusetts legislature approved a bill Tuesday that would require all residents to purchase health insurance or face legal penalties, which would make this the first state to tackle the problem of incomplete medical coverage by treating patients the same way it does cars.

Gov. Mitt Romney (R) supports the proposal, which would require all uninsured adults in the state to purchase some kind of insurance policy by July 1, 2007, or face a fine. Their choices would be expanded to include a range of new and inexpensive policies — ranging from about $250 per month to nearly free — from private insurers subsidized by the state.

Romney said the bill, modeled on the state’s policy of requiring auto insurance, is intended to end an era in which 550,000 people go without insurance and their hospital and doctor visits are paid for in part with public funds.

“We insist that everybody who drives a car has insurance,” Romney said in an interview. “And cars are a lot less expensive than people.”

Tuesday’s votes approving the bill — 154 to 2 in the House and 37 to 0 in the Senate — were the culmination of two years of politicking and several months of backroom negotiations, as rival health-care plans from Romney and the two Democrat-led chambers were hammered into one.

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