The chief federal job-safety enforcer has joined critics of the Environmental Protection Agency's approval of a new and possibly cancer-causing pesticide to combat fire ants in the South.

The protest by Dr. Eula Bingham, assistant secretary of labor for occupational safety and health, adds another dimension to EPA's approval of ferriamicide on an "emergency" basis this spring in Mississippi.

EPA decided last week to delay its approval, issued Jan. 30, after new Canadian research data was disclosed suggesting that ferriamicide poses serious risks to human health.

Bingham has raised questions about sex bias in the EPA approval decision, which forbade women of child-bearing age to handle the pesticide because of possible health risks.

Her questions about discriminatory regulation were based on research findings that a principal ingredient of ferriamicide had a serious adverse impact on the sperm count of male laboratory rats. Such data would indicate that the pesticide could be as devastating to male reproductivity as to female reproductivity and could cause birth defects in infants.

But Barbara Blum, deputy administrator of EPA who gave the Mississippi approval, defended her decision in a response to Bingham that was made public last week.

Blum's letter said that EPA toxicologists had interpreted test data on Mirex, a ferriamicide ingredient banned previously by the agency, to mean that pregnant women exposed to ferriamicide might bear abnormal children.

Blum said she did not favor any moves that would limit jobs available to women, but in the case of ferriamicide "I believe the trade-off... was essential."

Twice last year and again last month EPA had authorized a one-time-only application of ferriamicide against the bothersome fire ants this spring in Mississippi. Untested chemicals can be used if EPA finds an "emergency" situation.

Litigation by the Environmental Defense Fund prevented use of ferriamicide in 1978, and the delay announced last week by EPA could further postpone the chemical's use in the South.

Eight other southern states have similar emergency-use petitions pending at EPA. Thousands of acres in the region are infested by the fire ants, which attack humans and livestock and impede farming.

The states mounted a major legislative and public relations campaign to win EPA approval of ferriamicide, which was developed by Mississippi as a successor to Mirex.

Mirex was used against the ants for years before serious human health concerns were raised. The state of Mississippi, which had been the last manufacturer of the chemical, agreed to stop production last year.

The same chemical, however, is imported from Brazil for use by Mississippi as a component of ferriamicide, which, according to EPA, breaks up quickly after it is applied and poses no serious threat to humans.

The new Canadian research came to EPA's attention after the Jan. 30 approval for Mississippi. That data shows that a compound, photomirex, released as ferriamicide decomposes is from 10 to 100 times more toxic than Mirex.

Throughout months of debate and litigation over the new pesticide, EPA showed acute sensitivity to political demands for the use of ferriamicide. The agency was blitzed by southern senators and congressmen urging approval of the pesticide.

During the trial of the EDF suit last fall and subsequently, EPA has maintained that politics played no role in the ferriamicide decision.

Blum said on Jan. 30 and again last week as she disclosed the Mississippi delay that benefits of the fire ant eradication program had been weighed carefully against the potential risks to human health.

And while the federal district judge who tried the EDF suit declined to hold that politics had taken precedence, as EDF charged, the court record contains extensive examples of EPA's sensitivity to pressures from Capitol Hill.

At one point during the give-and-take over ferriamicide, Blum wrote Steven D. Jellinek, an assistant EPA administrator for toxic substances, to say that "Legally, we probably can't approve it."

But she also noted a "political problem" with crucial southern legislators who, as members of a House-Senate conference committee, controlled the fate of some pesticide-control law amendments that EPA wanted.

Blum wrote to President Carter on Feb. 22, 1978, laying out the political dilemma more explicitly, warning that members of Congress would be calling him about the pesticide, and pointing out that EPA had not had enough time to develop vital data on ferriamicide's health effects.

"We cannot say that ferriamicide is or is not safe for humans, domestic animals or non-aquatic species," she told Carter. But she noted that a congressional conferees' meeting, set for the following week, would determine the outcome of the administration's pesticide amendments.

"Senators Talmadge, Eastland and Allen, all anxious for EPA to approve the ferriamicide request, are on the conference committee," she advised Carter.

In addition to Sens. Herman Talmadge (D-Ga.), James O. Eastland (D-Miss.) and the late James Allen (D-Ala.), four other legislators from the fire ant region were among the 24 conferees.

The amendments were adopted. And not long afterward, EPA made its first emergency approval of ferriamicide for Mississippi -- which was then delayed by the EDF litigation.

In another note to Jellinek, Blum said of approving ferriamicide: "If it's a political decision, we want to make the most of it."

Before the pressure became more intense on EPA early last year, Jellinek in November 1977 already had moved to try to defuse some of the political fire.

In a memo to Joan Nicholson, head of EPA's Office of Public Awareness, he said that Mirex should not be included as a topic of a film EPA was preparing on pesticides.

"It is a highly emotional, very political and often irrational subject," Jellinek said. "If one is looking for a pesticide illustration I would recommend aldrin/dieldrin [also banned by EPA] as far more appropriate.... EPA should consult with interested congressmen or staff about this film project, particularly if a pesticide is under consideration as the featured chemical."

And at another point, in a bow to Eastland, dean of the Senate before his retirement last month, Blum alerted White House congressional liaison director Frank Moore that she would personally contact the Mississippian as part of a "political notification plan" to tell him of ferriamicide's approval.