SACRAMENTO — Even as the sweet strawberry harvest reaches its peak here, a bitter disagreement has erupted between the State Department of Pesticide Regulation and a scientific review committee over the approval of a new chemical, the outcome of which could affect farmers across the country.

In a report and in public testimony Thursday before the State Senate Food and Agriculture Committee, members of the review committee said the state’s decision to approve the new pesticide, methyl iodide, was made using inadequate, flawed and improperly conducted scientific research.

“I’m not in blanket opposition to the use of pesticides, but methyl iodide alarms me,” said Theodore A. Slotkin, a professor of pharmacology and cancer biology at Duke University Medical Center and a member of the scientific review committee. “When we come across a compound that is known to be neurotoxic, as well as developmentally toxic and an endocrine disruptor, it would seem prudent to err on the side of caution, demanding that the appropriate scientific testing be done on animals instead of going ahead and putting it into use, in which case the test animals will be the children of the state of California.”

But farmers here — who grow nearly 90 percent of the nation’s strawberries, a $2 billion a year industry — say the state’s proposed regulations would far exceed those set by the federal government for the chemical, which they argue would be deployed safely and only when needed.

“The 500-plus growers of strawberries in the state are largely family farmers who live where they grow,” said Carolyn O’Donnell, spokeswoman for the California Strawberry Commission. “When they make decisions about how and where they farm, they make those decisions with the health and safety of workers and the community in mind.”

For decades, farmers injected another chemical, methyl bromide, into the soil before planting strawberries. Then the Montreal Protocol international climate treaty banned methyl bromide, saying it had been found to deplete ozone. That sent regulators, farmers and the chemical industry scrambling for an alternative.

They found methyl iodide, a chemical less harmful to the ozone, but with more potential hazards to human health. In 2007 the chemical was approved by federal environmental regulators to the chagrin of many scientists. More than 50 chemists and physicians, including members of the National Academy of Sciences and Nobel laureates, had asked the federal Environmental Protection Agency not to approve the chemical.

Despite federal approval, California requires that new pesticides go through a second review, a process that federal regulators have said they are watching closely and that could lead to a re-evaluation by the Obama administration.

California has provisionally approved methyl iodide and will issue a final decision after the public comment period ends June 29.

During Thursday’s hearing, pesticide regulators voiced confidence in the scientific basis for their decision.

“The review associated with this material is the most robust and extensive in the history of the department,” said Mary-Ann Warmerdam, director of the state regulatory agency.

Ms. Warmerdam said that based on the available data, the chemical could be used safely with precautions like respirators, impermeable tarps and extra restrictions on use around schools, businesses and homes.

The scientific review committee, which was commissioned by the regulatory agency, vehemently disagreed.

“This is without question one of the most toxic chemicals on earth,” said John Froines, professor of environmental health sciences at the University of California, Los Angeles. “You don’t register a chemical when you don’t have the necessary information you need.”

Once out in the environment, neurotoxic chemicals like methyl iodide contribute to neurodevelopment disorders including learning disabilities, conduct disorders, autism spectrum disorders and attention-deficit hyperactivity disorder, said Dr. Slotkin, who called such health disorders a “silent pandemic.”

State Senator Dean Florez, a Democrat who leads the Food and Agriculture Committee, said, “If we’re going to have to make the decision about using a toxic chemical like this, I’d like elected officials in the state of California to make this decision, not a non-elected agency and an outgoing Republican administration.”