On Jan. 19, the last full day of the Carter administration, as departing officials were loading packing cartons and taking photos off the walls, the Labor Department announced a major decision in the long, fierce legal battle over protection of industrial workers against lead poisoning.

For Eula Bingham, the Carter administration's strong-willed head of the department's Occupational Safety and Health Administration (OSHA), the decision was the last word in a five-month struggle over a strict lead-exposure standard affecting workers at hundreds of plants in 46 industries, from copper smelting to shipbuilding.

But, within a week after the administration changed hands, industry attorneys were able to persuade the Labor Department to change its mind.

The Jan. 19 decision by Bingham should be temporarily set aside, the Labor Department said in a Feb. 4 petition to the Court of Appeals for the District of Columbia, to give the incoming Reagan team a chance to correct any errors Bingham may have made.

The sudden conversion was even more impressive in that it happened when the Labor Department and OSHA were headless. Incoming Reagan administration officials were not on the job, and the highest-ranking Labor official at the meeting of lawyers that led to the change was acting solicitor Alfred G. Albert.

The Court of Appeals has not ruled on the petition, which is opposed on behalf of affected industrial workers by attorneys for the United Steelworkers of America, who were not invited to the meeting between Labor and industry lawyers.

Industry attorneys, meanwhile are looking beyond a mere reconsideration of the Jan. 19 rule to what they see as a golden opportunity to reverse it.

Both sides in the dispute agree the lead case indicates the dramatic shift in business regulation that has begun under President Reagan. In many ways, the lead standard is OSHA's most ambitious attempt to control chemical hazards in industrial plants since the agency was formed in 1971.

Union sources say that, with the lead decision, OSHA finally lived up to its promise. Company sources say it lived up to their worst fears.

Lead is one of the most common industrial substances, a vital ingredient in many manufacturing processes and a by-product of others. It also has been branded for centuries as a poison when inhaled or swallowed in sufficient amounts.

The effects of lead poisoning range from dizziness and insomnia to sterility, central nervous system damage, kidney failure and, ultimately, death.

At least 800,000 U.S. workers are exposed to varying amounts of lead, and a hotly disputed issue in the lead case was the level of protection necessary to prevent irreversible health damage.

OSHA's final lead standard was issued in November 1979, after Bingham, a strong advocate of worker health protection, had taken charge of the agency. After 39 days of public hearings, OSHA set a standard limiting a worker's daily exposure to 50 micrograms per cubic meter of air.

What made the lead standard unique, however, were two unprecedented enforcement decisions by OSHA.

First, OSHA ruled out the use of respirator face masks as a means of achieving permanent compliance with the exposure limit. Respirators could be used temporarily, but companies would be required eventually to make engineering changes in their plants, installing hoods, large air filters or other equipment, to reduce airborne lead.

Companies also had the option of reducing the time workers were exposed to lead by rotating them on and off the job more frequently.

The difference in the costs of the two strategies can be immense for "dirty" plants because respirators cost a fraction of the price of the engineering changes OSHA was demanding.

OSHA was persuaded by union complaints about respirators, which are uncomfortable at best and can be a severe handicap for workers who have breathing problems.

Second, OSHA insisted upon a "worker removal policy." Whenever medical tests showed a worker had abnormally high levels of lead in the blood, the worker would have to be transferred to an uncontaminated part of the plant, or sent home if necessary, until the lead levels in the blood dropped below OSHA's safety standard -- and the worker would be entitled to full pay and benefits, plus seniority protection, up to 18 months.

A large number of industries challenged OSHA's standard, but in a 2-to-1 decision last August, the Court of Appeals ruled in OSHA's favor on every major point except one. The case has been appealed to the Supreme Court.

The key to the appeals court's decision was its conclusion that OSHA was entitled to free-swinging discretion in carrying out the mandate it received in 1971 from Congress: to assure "to the extent feasible, on the basis of the best available evidence, that no employe will suffer material impairment of health or functional capability. . . ."

OSHA's regulatory task is "essentially legislative" and often rooted in "highly speculative" inferences from complex scientific and economic data, the court said. It added that a court simply is not competent to second-guess a regulatory agency as long as its decisions fall "within a zone of reasonableness."

"We do not know to a scientific certainty the precise levels of air-lead exposure or blood-lead content at which different lead-induced diseases occur," the court said. But in the end it relied on the scientific studies OSHA used in setting the lower standard.

Since Congress did not spell out how the balance should be drawn between protecting workers and avoiding "unfeasible" burdens on industry, the court was reluctant to draw the line.

However, it did say OSHA had not produced enough evidence to show the lead standard was technologically and economically feasible for the 46 industries where lead compounds are components or byproducts of manufacturing.

The court's August decision gave OSHA six months to review this issue. When Bingham issued her Jan. 19 findings, essentially upholding OSHA's original position, in just five months, industry claimed foul.

They called her finding a "charade" and a "midnight regulation" hastily issued in the final hours of the Carter administration.

The reversal was just as hasty. OSHA solicitor Albert, the agency's top-ranking officer in the days after Inauguration Day, has since retired, but another OSHA attorney who attended the post-inaugural meeting said the industry made this argument to Albert and his staff:

"You're not decision-makers, you're lawyers, and all you are concerned about is steering a neutral course between two administrations. The new administration will have a different philosophy. Join us in asking the court to say its hand [on the standard for the 46 industries] until the new administration is in place."

OSHA attorneys were "acutely uncomfortable" at the meeting, in part because one of the industry attorneys was William J. Kilberg, Labor Department solicitor in the Ford administration and a former member of the Reagan transition team dealing with the Labor Department, the agency attorney said.

"But he [Kilberg] is also opposing counsel, and you've got to deal with him," an OSHA source said.

Kilberg, in an interview, said, "I don't think they [the OSHA attorneys] were pressured or intimidated. We aren't in a position to get a sweetheart deal. We're before those three judges" on the Court of Appeals.

"We simply felt that with a new administration, we might have an opportunity for a less biased, fairer hearing," Kilberg said.