Workers at a Midwest lead processing plant were exposed to more than 100 times the allowable levels of lead in the air and then given repeated medical treatments by a company employed doctor that endangered their kidneys and other internal organs, federal occupational health officials have charged.

The Occupational Safety and Health Administration made the charges Wednesday in levying the heaviest fine in the agency's history for worker health violations against NL Industries, the nation's larges lead producer.

OSHA recently moved to lower acceptable exposure levels of lead in the air over sharp industry objections. Medical tests have shown high blood lead levels cause damage to the central nervous system and long-term exposure to the metal at high levels can cause death.

OSHA officials said yesterday that NL Industries allowed workers in its Beech Grove, Ind., lead reprocessing plant to work in air that exceeded permissible lead levels by more than 100 times on occasion and that lead levels throughout the plant regularly exceeded federal limits by two to four times.

When workers at the plant turned up with high levels of the toxic metal in their blood a doctor hired by the company regularly used a drug therapy treatment on them which medical experts have condemned as hazardous, federal officials said. Documents filed by OSHA inspectors with the firm said that workers at the plant were never told why they were dosed with the drug or given an explanation of its dangers.

Federal health officials have requested the worker health records from NL Industries in an administrative subpoena but the company has refused to turn them over, the OSHA citation said.

The fines - totaling $154,000 - are the first ever levied by OSHA under a ruling enacted in July that requires employees to keep and provide to federal inspectors records of worker exposure to toxic substances on the job.

Spokesman for NL Industries said at the company's New York City headquarters yesterday that they believed the OSHA citation was "without merit." But they declined to comment further because they said the citation was presented at Beech Grove and they had not yet examined it.

Richmond Unwin, director of communications for the company, said medical treatments of employees at the Beech Grove plant "followed prescribed medical practices."

Dr. Frederic A. Rice, who has been employed by NL Industries to treat workers at the plant since 1971, said in a telephone interview that he is continuing to use a treatment called "chelation therapy" to lower lead levels in workers' blood. "Until a better treatment comes along I don't know what else to do," he said.

Rice was hired as an "outside consultant" by NL Industries, said John Roper, the company's corporate safety director.

"What he is going is his business," he said. "We don't tell him what to do."

According to occupational health experts, chelation therapy is a last-resort practice that can, if done repeatedly, damage kidneys and other intrnal organs. Federal occupational health experts condemned the practice years ago, they said.

"You can either chelate someone to get rid of the lead in a hurry to reduce exposere," said Dr. Theodore Thoburn, a federal research and lead expert. Repeated chelation, he said, will not halt rising blood lead levels for those continuously exposed to the metal. In addition, when the process is repeated, he said, patients face increased risk of kidney damage.