Just hours after a conference committee passed a landmark workers' compensation reform bill Thursday, Assembly Democrats said they would introduce another bill to regulate rates charged by insurance companies.

"We plan to put the issue before the governor's desk," said Assembly Speaker Fabian Núñez, D-Los Angeles. "California businesses need rates to go down and that won't happen unless we make it happen."

Only rate regulation, Democrats say, will assure that the cost-cutting reforms in the bill expected to pass the full Legislature Friday will actually translate into expected savings for businesses that have seen their insurance premiums double and triple since 2000.

Republican Gov. Arnold Schwarzenegger, who pushed hard for the new reforms, has steadfastly opposed rate regulations, saying lower rates will come from the increased competition caused by the reforms.

Democrats dropped rate regulations from negotiations for the larger bill, but Núñez said Thursday they "do not trust the market forces" to bring about lower rates.

Although Schwarzenegger opposed regulating premiums, Núñez said the Democrats' proposal is for a two-year trial period and isn't "about regulating the industry forever. We think we're sending the governor a bill he can sign."

A spokesman for the governor could not be immediately reached for comment.

Democrats planned to introduce the bill Thursday in the Assembly Insurance Committee.

A six-member conference committee approved the reform package at 3:30 a.m. Thursday, handing Schwarzenegger a political victory in overhauling the system with high costs for employers while paying some of the nation's lowest benefits to injured workers.

While also holding off rate regulation, Schwarzenegger also won on a provision that would allow insurers and employers to select pools of doctors injured workers must use.

Labor and attorneys groups criticized the lack of rate regulation and anything that forces an injured worker to see a company physician.

"Free choice of doctors is very important to an injured worker," said David Schwartz, president-elect of the California Applicant Attorneys Association, a group of lawyers who represent injured workers.

Schwarzenegger worked with legislators for weeks to reach a deal, while simultaneously threatening them with a proposed initiative that would ask voters to change the workers' compensation system. Much of Tuesday and Wednesday, he met with Assembly and Senate Republicans, aiming to reach a two-thirds majority vote that would make the reforms effective immediately upon his signature.

Assemblyman Rick Keene, a Chico Republican and a conference committee member, praised the bill for cutting costs while making "sure the emphasis is not on people trying to get cash awards for workers' comp injuries, but on folks getting better and getting back to work."

As a safety net, supporters of a proposed initiative, pushed by Schwarzenegger and $1.6 million from his personal campaign fund, announced Wednesday they had gathered more than 1 million signatures and would submit them Friday to put the issue on the November ballot if the Legislature didn't pass the reform plan.

But that appears unlikely.

"I gotta tell you, there's no question this is not a perfect bill," Núñez said. "What it is is an attempt to reach a compromise on a workers' compensation system that's broken, a system that doesn't serve injured workers very well and a system that is costing a great deal of money with premiums increasingly on the rise."

Workers' compensation costs have soared in recent years in California, from $6.4 billion in claims paid in 1997 to an estimated $25 billion last year. The average cost of dealing with workplace injuries also rose dramatically, from $2.68 per $100 of payroll in 2000 to $6.30 per $100 in 2003 -- the highest rate in the nation.

Most systems nationwide are more limited than the one in California, which covers all industries and all workers, including employees of small businesses. The state also makes it easier for workers to get benefits, covering injuries and occupational diseases that other states do not.