CHICAGO – Looking to bolster the fight against childhood lead poisoning, the U.S. Environmental Protection Agency last month approved a tough new rule aimed at clearing the nation’s air of the toxic metal.

A key part of the initiative is a new network of monitors that will track lead emissions from factories. But the Bush administration quietly weakened that provision at the last minute by exempting dozens of polluters from scrutiny, federal documents show.

Critics say the change undermines a rule that otherwise has been widely hailed as a powerful step forward in protecting children’s health.

In Illinois, at least a dozen factories that would have been monitored could now fall through the cracks, the state EPA estimates, including a steelmaking-waste recycler on Chicago’s Southeast Side and a lead-acid battery manufacturer in Naperville.

The federal rule was prompted by compelling research showing lead is more dangerous than had been thought. Even low levels of the toxic metal in young children have been linked to learning disabilities, aggression and criminal behavior later in life. Many scientists say there is no safe level of exposure.

Faced with a court order to act more aggressively, the U.S. EPA last month lowered the maximum amount of lead allowed in the air. The new standard, 0.15 micrograms per cubic meter, is 10 times more stringent than the old standard set in 1978.

To help meet the new limit, the EPA had planned to require lead monitors next to any factory emitting at least a half-ton of lead a year. But after the White House intervened, the agency raised the threshold to a ton of lead or more, according to e-mails and other documents exchanged between the EPA and the Office of Management and Budget.

As a result, dozens of factories won’t be checked regularly. Federal and state officials debate the exact number, but a Tribune review of EPA records found the number of U.S. plants monitored could drop by nearly 60 percent, from 203 to 87.

“This sleight of hand by the administration ignores major sources of a dangerous neurotoxin,” said S. William Becker, executive director of the National Association of Clean Air Agencies.

President-elect Barack Obama’s administration could try to amend the lead rule, but that process would take months to complete.

National lead emissions have dropped 97 percent under the old standard, largely because lead was removed from gasoline. But cement plants, smelters, steel mills and other factories still emit about 1,300 tons of lead into the air each year, according to the EPA.

After the tiny lead particles settle to the ground, they can stay there for years. Exposure usually occurs when people, especially children, handle or play with contaminated soil and put dirty hands into their mouths.

“If we can keep bringing down blood-lead levels in kids, there could be considerable benefits over the years to a wide swath of our population,” said Bruce Lanphear, a researcher at Simon Fraser University in British Columbia and member of a scientific panel that urged the EPA to set tougher lead standards.

Dozens of monitors scattered across the country already check lead levels in the air, but the EPA estimated it would take dozens more to track emissions from polluters releasing at least a half-ton of lead.

Industry lobbyists waged a fierce battle against the new standard and the additional monitoring of factories. They argued that lingering dust from leaded gasoline and lead paint are a much bigger threat to children than ongoing industrial emissions.