SACRAMENTO - California Republicans and moderate Democrats joined forces this week to approve a bill that would prevent local governments from banning genetically modified crops.

The bill, SB1056, by Sen. Dean Florez, D-Shafter, passed the Assembly with a 46-19 bipartisan majority.

The legislation, backed by the California Farm Bureau Federation and large agribusiness concerns such as Monsanto, comes in response to moves by Marin, Mendocino, Santa Cruz and Trinity counties to ban bioengineered crops.

Opponents of genetically engineered foods say they are potentially unsafe and pose a business threat to organic farmers who could lose organic certification if their crops were contaminated by biotech seeds.

The bans prompted Florez to introduce legislation that would give the state exclusive control over the regulation of field crops.

While the four counties that already have bans in place would be exempt from the bill, California's remaining 54 counties would be required to look to the state for regulation of the industry, even though the state does not have any regulation on the books.

Supporters say state regulation is unnecessary because the industry is already highly scrutinized by the federal government, but opponents say recent bans on genetically engineered crops should signal the state that better regulation is necessary.

''If there's strong state regulation that adequately protects farmers, the environment and consumers, there should be no need for local initiatives,'' said Rebecca Spector, a spokeswoman for the Center for Food Safety. Florez told The Chronicle in July that he planned to add to the bill statewide regulations on genetically engineered seeds, to give local governments the assurance that the industry is being regulated.

He said Thursday that he has been negotiating with opponents for a two-year moratorium on laws affecting bioengineered crops -- which he called ''a pause until we could get that state policy in place'' -- but negotiators were unable to come to an agreement.

''Everyone was clear -- we were either going to compromise or move the bill,'' said Florez. ''The enviro folks made a bad bet.''