The Environmental Protection Agency, caught between a major chemical company and a group of influential legislators, has decided not to approve the use of a controversial and dangerous pesticide, ferriamicide, against the fire ant in nine southern states.

Rather than flatly rejecting the request for a conditional-use permit for ferriamicide, the EPA announced yesterday that it will join the Department of Agriculture in holding a June symposium to consider any new scientific or legal data on the pesticide.

The EPA's decision means that ferriamicide will not be available for aerial and ground application this spring, despite the urgings of members of Congress from states infested by the bothersome, migratory ant.

Ferriamicide is made from Mirex, a long-lasting pesticide that is thought to cause cancer and birth defects. Ferriamicide backers contend that it degrades quicker and is less dangerous to humans than Mirex, a product that Mississippi voluntarily canceled just before EPA was about to ban it.

Led by Sen. Thad Cochran (R-Miss.), senators from the ant-plagued states had urged EPA administrator Anne M. Gorsuch this month to clear a Mississippi request for approval of ferriamicide, which is manufactured in a state-owned plant.

But the American Cyanamid Co., which produces Amdro, a much more expensive pesticide that EPA has authorized for use against the ant, was pushing the other way, urging that the agency reject the Mississippi application.

Mirex had been used for 15 years against the ant with only limited success. Fire ants have infested more than 230 million acres in the South, disrupting farm operations with mounds they build, and biting humans and animals.

After the Mirex flap five years ago, EPA approved ferriamicide for use under strict rules. The pesticide was not used, however, after EPA was challenged in court and new scientific studies suggested it was even more toxic than Mirex.

EPA's decision yesterday pleased neither side in the dispute. Cochran said "it has to be a disappointment . . . . Amdro costs about six times more than ferriamicide." A Cyanamid spokesman noted that EPA's indecision leaves the door open for later approval of ferriamicide.

But Rep. George E. Brown Jr. (D-Calif.), chairman of a House Agriculture subcommittee that oversees pesticide regulation, warned that EPA should reconsider previously banned or suspended chemicals only if "substantial" new scientific evidence suggests they can be used safely.

"If EPA is to retain public confidence, the agency's decisions must be well supported by scientific findings," he said. "I want to assure Gorsuch that if she continues to make decisions based on sound science, she will have my strong support and, I believe, the support of the entire Agriculture Committee."

Brown said that "a hasty decision" on ferriamicide "would have been a clear signal" that the agency might be favorably disposed to reconsidering previously banned or canceled products such as DDT and other chlorinated hydrocarbons.

The subcommittee chairman indicated that he still is concerned about the safety of Cyanamid's Amdro, which has recently come under fire because of new questions about its potential effect on human health. Brown said he is urging the company to make "early public disclosure" of health and safety data about the product.