The changeover to an assigned risk program was initiated by the previous insurance commissioner, Julie Bowler. It commenced last month after Ms. Bowler won a court battle in August.

Her move to an assigned risk program was challenged in court by Commerce Insurance, Arbella Mutual Insurance Company and the Center for Insurance Research, as well as seven insurance agencies and brokerages.

The commissioner was supported by the American Insurance Association with the Massachusetts Insurance Federation, the Property Casualty Insurers Association of America, the Public Interest Research Group and a number of insurers who filed a "friend of the court" brief.

The changeover was planned to go into effect April 1 for newly licensed drivers or those coming in from out of state, and expand in increments over a three-year period.

When that timetable was announced, Stephen D'Amato, a consultant to the Cambridge-based Center for Insurance Research, said the new assigned risk plan would not work with the current "fix and establish" system, in which the department mandates the auto rates each year.

He told the NU Online News Service that the new Democratic governor, Deval Patrick, who took office this month, would have to look into delaying implementation to study the consequences of the program.

"And I think it is most important that any decisions about who to put in the assigned risk plan be made on driving record only, and not on other factors based primarily on income," he said.

Acting Commissioner Murphy said he acted to consider "both the short- and long-term implications of those rules on the Massachusetts private passenger automobile market with least the disruption to consumers and the insurance industry."

In reaction, PCI said his announcement was, "disappointing but not unexpected given the pressures that reform opponents have put on the new administration."

It called the proposed rule changes to create an assigned risk pool "essential to making the auto insurance system operate in a fair and equitable manner and in compliance with Massachusetts law."

PCI added that former Attorney General Reilly and Commissioner Bowler had "demonstrated conclusively that the operations of CAR do not comply with the law and have been responsible for driving numerous companies out of the state, out of business or into insolvency."