Gov. Jim Florio's auto insurance reform plan has passed another level of legislative approval, despite lack of support from Republicans, who criticized the measure's swift review.

The plan, which promises to save motorists at least 20 percent on their auto insurance bills by March 1991, moved to the floor of the Assembly, where a vote is scheduled for today. The 80-page bill was introduced in the lower house on Jan. 25, and was debated in five hearings by a joint legislative committee."This legislation brings long-awaited, meaningful relief to New Jersey motorists who are sick and tired of paying astronomical auto insurance rates that are unjustified, unfair and unaffordable," said Assembly Speaker Joseph Doria, D-Hudson.

Mr. Doria told the appropriations committee that the measure's quick movement "is indicative of the new spirit of cooperation that is characterizing the New Jersey state government in 1990."

Republicans on the appropriations panel, however, charged that the bill was being pushed through too quickly and said it will not accomplish its goals.

"I'm disappointed in the process," said Assemblyman Rodney P. Frelinghuysen, R-Morris. "The rapidity with which this bill is running through the legislative process does not show concern for the motorist. It is being done to give the public perception that something is being done."

The committee vote went along party lines. All nine Democrats voted for the bill, three Republicans voted against it, and three Republicans abstained. Both houses of the Legislature are controlled by Democrats.

The Florio plan would dismantle the troubled Joint Underwriting Association pool for high risk drivers, which is $3.1 billion in debt. Gov. Florio wants insurance companies to pay off $1.4 billion of the debt, saying they have unfairly taken advantage of the poorly operated JUA.

The rest of the debt would be paid off with higher auto registration fees and assessments on professions that benefit from auto accidents. The JUA would be replaced by a much smaller assigned risk pool for bad drivers.

Because the JUA is in such bad financial shape, each motorist pays $222 a car each year to keep it in business. The Florio plan would wipe out this charge by March 1991.

In addition, the plan would allow motorists to use health insurance policies to pay for auto accident injuries. Officials say this could save about $40 on each auto insurance policy.

Republican members of the committee, however, noted that the measure could be stymied by a threatened lawsuit by the insurance industry, which does not want to pay the $1.4 billion in assessments. In addition, they charged that health insurance costs could go up if that becomes the primary coverage for many accidents.

The Republicans said the bill does not guarantee that insurance companies won't pass on the $1.4 billion assessment and does not deal with the cause of high insurance in New Jersey.

The bill's fast process also drew criticism from a member of the audience who claimed to be representing a group called "Save Our Coverage."

"You're putting this thing on a freight train and railroading it past the citizens of New Jersey," shouted Garrison Pomeroy of Cherry Hill. Mr. Pomeroy, who said his group numbers 3,000, said the bill reduces insurance coverage and allows the industry to increase rates.

Assemblyman Robert Menendez, D-Hudson, defended the bill, calling the Republicans "the angels of alarm."