Farm groups joined the manufacturer of the popular herbicide atrazine Tuesday in accusing the Obama administration of bowing to environmentalist pressure in initiating a review of the chemical’s safety.

The Environmental Protection Agency under the Bush administration certified the weedkiller for continued use, but the agency said last month that it would take another look at possible health risks.

Agency officials told a six-member panel of scientific advisers Tuesday that they wanted to review new data from studies of the chemical’s cancer-causing potential, including the results of research into the health of agricultural workers and pesticide applicators in Iowa and North Carolina. Atrazine is used on about 60 percent of Iowa’s corn acreage to control weeds other chemicals may miss.

The agency plans to use the data to decide whether to revise its safety assessment of the pesticide, said Tina Levine, director of the agency’s health effects division.

The review will extend through 2010.

Officials with the pesticide’s maker, Syngenta Crop Protection Inc. of North Carolina, told the panel that the additional study was unnecessary. Syngenta downplayed concerns raised by an environmental group, the Natural Resources Defense Council, that water supplies may be contaminated with the chemical at higher rates than previously thought.

“We strongly feel that the new information that has been sparked by the attacks of the anti-atrazine group and in the press do not justify reopening the review of atrazine,” said Janis McFarland, head of regulatory affairs for Syngenta Crop Protection in North America.

Gary Marshall, chief executive of the Missouri Corn Growers Association, said the study “is being driven by some folks out there who are anti-farming, anti-agriculture.”