Webster-based Commerce Insurance Company will definitely oppose the bill, said Jim Ermilio, Commerce senior vice president. He said the current "fix and establish" rate system is one of the reasons the state has one of the lowest rates of uninsured drivers.

"This strikes me as a bill that was written by some of the national companies to make it lucrative for them to enter Massachusetts. It does not surprise me that the governor is supporting a bill backed by national companies, because based on everything we have read he has national aspirations."

Mr. Ermilio said that if a national writer wants to come in and lower rates they can do that already under the current regulatory regimen. He sees the bill as leading to "bait and switch" tactics that will lure drivers with lower rates at first and provide hikes later.

But pro-reform forces remain optimistic.

Mr. O'Brien noted that Democratic Senate President Robert Travaglini has said auto insurance reform is one of his top three priorities in a session that is just hitting its stride after budget passage. The lower house is also controlled by Democrats.

In introducing his proposal last week, Mr. Romney said that average savings for the state's better drivers will amount to 5 percent, or from $52 to $119 on a statewide basis.

"With so few insurers doing business here, we can no longer pretend that our system is healthy and benefiting our system," Mr. Romney said.

The governor said that the legislation will allow insurers rate flexibility for all coverages but would cap any maximum rate increase for liability coverages at 15 percent annually.

The legislative initiative follows court action by several of the state's insurers led by Commerce, which has blocked efforts by State Insurance Commissioner Julie Bowler to reform the residual market through regulation. The insurers obtained an injunction arguing Ms. Bowler lacked the authority to make such changes.

Mr. O'Brien said the proposed legislation will give the commissioner the specific authority, while the possibility remains that Ms. Bowler will win her court fight.