BILLINGS — A proposed standard for federal cleanup of asbestos contamination in Libby concludes that even a tiny amount of the material can lead to lung problems — a benchmark far more rigorous than any in the past and one that the industry says could force expensive and unnecessary cleanups across the country.

The Environmental Protection Agency’s new proposal for Libby, where asbestos dust has killed hundreds of people, would be 5,000 times tougher than the standard used in past cleanups addressing airborne asbestos.

W.R. Grace & Co., the Maryland chemical company blamed for the pollution from its vermiculite mine that operated for decades, is pushing back against the proposal, suggesting sites across the country could be subjected to costly cleanups.

The Superfund cleanup in Libby has cost at least $447 million since 1999 and is expected to last several more years.

Experts say the proposal, which appears in a risk study on the asbestos in Libby, is a move long sought by advocates and fiercely resisted by the industry. An EPA board met to discuss Grace objections to the proposal this week.

“In many respects it would be like banning it, getting it so low,” said former assistant U.S. Surgeon General Richard Lemen, who teaches at Emory University in Atlanta. “EPA is being realistic and saying, ‘Look, we know there’s asbestos out there, and we’re not going to get rid of all of it, but let’s put our concentration as low as we possibly can.”’

EPA officials didn’t respond to questions about the nationwide consequences of the proposal, which says airborne asbestos concentrations exceeding 0.00002 of a fiber per cubic centimeter pose a health risk. The EPA has previously taken action only when the substance was airborne in amounts greater than one-tenth of a fiber per cubic centimeter.

But the Government Accountability Office has said the standard could affect some of the 200-plus industrial sites in 40 states that also received asbestos-tainted vermiculite from Libby. More than 20 of those sites, posing the highest health risks, have already been cleaned once. Most were processing plants where asbestos was heated at high temperatures so it could expand and be used for insulation in millions of homes.

The GAO and asbestos experts said the EPA risk assessment could force more cleanups. And Grace representatives and health officials said the EPA proposal could apply to other types of asbestos found in communities across the country.

In a letter to the EPA last week, Grace Vice President Karen Ethier said the standard would have “inevitable” consequences beyond Libby.

“That broad application will, in turn, result in enormous, unexpected and unnecessary costs to building owners, farmers and other property holders, including the federal government,” Ethier said.

Manufacturing and trade groups and federal agencies including the White House Office of Management and Budget also have raised questions about the EPA proposal. They said the proposed threshold falls below even background asbestos levels seen in parts of the country.

Although the sale and manufacture of asbestos-containing materials is tightly regulated, the government has never established a safe level of human exposure for the type of the mineral found in Libby. While there are general cancer-based exposure limits for asbestos set by the Occupational Safety and Health Administration, the EPA proposal for the first time sets a risk level for non-cancer illnesses, such as the debilitating and potentially fatal lung disease asbestosis.

That’s a crucial issue in Libby, where a vermiculite mine and processing plants operated by W.R. Grace for three decades left the town coated in asbestos dust that has killed an estimated 400 people and sickened at least 1,700 more. Health experts say the death toll is bound to rise because of the long latency period of asbestos-related illness.

The vermiculite was mined by Grace from a mountain outside town and shipped across the country for use as insulation, fertilizer, fireproofing material and other commercial products.

The mine closed in 1990.

Health problems first noticed in mine workers have since become pervasive in Libby, affecting spouses who laundered their husbands’ dust-covered clothes, generations of residents who played as children near Grace’s processing plants and others.

In public testimony and filings with the EPA, Grace has argued that less-severe lung problems considered a sign of asbestos disease can be confused with other health problems, such as obesity. The company maintains that the science used by the EPA to craft its proposal was flawed and has urged the agency to do more research before moving forward.

The air is far cleaner in Libby today than it was when the EPA first arrived, removing thousands of truckloads of contaminated soil and replacing it with clean topsoil. But the agency has acknowledged some people in Libby are still at risk, particularly landscapers and others who stir asbestos-laden soil.

The EPA is to make a final decision on the standard for Libby sometime next year.

Earlier this week, the agency’s science advisory board reviewing the proposal requested only limited revisions after Grace asked to send it back for further study.

Agnes Kane, a member of the EPA advisory board and chair of its Libby asbestos panel, said the government and Libby can’t afford to wait.

“We certainly can’t sit around and wait for these types of studies to be done,” Kane said. “We have to use our best scientific judgment. It is necessary to proceed with the remediation of that Superfund site.”