WASHINGTON — First you paid to insure your car. Soon you may have to add health insurance premiums to that stack of monthly bills as well.

In a revamped health care system envisioned by senators, people would be required to carry health insurance just like motorists must get auto coverage now. The government would provide subsidies for the poor and many middle-class families, but those who still refuse to sign up would face fines of more than $1,000.

The details were unveiled Thursday in a health care overhaul bill supported by key Senate Democrats looking to fulfill President Barack Obama's top domestic priority.

The Congressional Budget Office estimated the fines would raise around $36 billion over 10 years. Senate aides said the penalties would be modeled on the approach taken by Massachusetts, which now imposes a fine of about $1,000 a year on individuals who refuse to get coverage. Under the federal legislation, families would pay higher penalties than individuals.

Called "shared responsibility payments," the fines would offset at least half the cost of basic medical coverage, according to the legislation. The goal is to nudge people to sign up for coverage when they are healthy, not wait until they get sick.

In 2008, employer-provided coverage averaged $12,680 a year for a family plan, and $4,704 for individual coverage, according to the Kaiser Family Foundation's annual survey. Senate aides, who spoke on condition of anonymity because they were not authorized to speak publicly, said the cost of the federal plan would be lower but declined to provide specifics.

The legislation would exempt certain hardship cases from fines, which would be collected through the income tax system.

The new proposals were released as Congress neared the end of a weeklong July 4 break, with lawmakers expected to quickly take up health care legislation when they return to Washington. With deepening divisions along partisan and ideological lines, the complex legislation faces an uncertain future.