The prospects for a controversial proposal to allow roughly 150,000 undocumented immigrants to obtain driver's licenses darkened considerably yesterday, as Governor Mitt Romney came out against the idea and as the bill's sponsor acknowledged that "it doesn't look as if the legislation could become law."

Nicole St. Peter, a Romney spokeswoman, said that 37 people called the governor's office yesterday to urge him to oppose [Eugene L. O'Flaherty]'s proposal, but that Romney had not been told of the calls when he altered his stance.

Advocates point out that allowing undocumented immigrants to get driver's licenses will clear the way for them to get driver training and auto insurance, making all motorists safer. The Massachusetts Association of Chiefs of Police pointed out that drivers with licenses are much less likely to flee the scene of a crash. Supporters also argue that un documented immigrants are an integral part of the state economy and should be allowed to legally drive to and from work.