BILLINGS, Mont. - A long-delayed U.S. government cleanup plan for a Montana community where asbestos contamination has sickened thousands would leave the deadly material in the walls of houses, underground and elsewhere - stirring worries among residents and state officials about future exposures.

Tuesday's proposal, for the neighboring mining towns of Libby and Troy, calls for asbestos-containing vermiculite to be left in place where the Environmental Protection Agency says it presents minimal risk and can be safely managed.

But some Libby residents said the asbestos inevitably will escape during future excavation work, home renovations and accidents such as fires.

It's been more than 15 years since media reports revealed widespread illness caused by asbestos dust from a W.R. Grace and Co. vermiculite mine outside Libby, about 50 miles south of the Canada border. Health workers have estimated as many as 400 people have died and almost 3,000 have been sickened from exposure to the contamination.

"We've left a lot of this behind in these houses, and you always have the potential of people opening up that wall and running into it," said Mike Noble, who worked for 21 years for Grace in Libby as an electrician and suffers from a lung disease caused by asbestos. "The EPA is unwilling to address that because the EPA is saying it's safe as long as nobody touches it."

State regulators aired similar concerns in an April 2 letter to the EPA obtained by The Associated Press.

Montana Department of Environmental Quality Division Administrator Jenny Chambers said it was unclear how the remaining contamination would be monitored or what would happen when "currently inaccessible waste becomes accessible."

Vermiculite from the Grace mine was used as insulation in millions of houses across the U.S. In the Libby area, asbestos-tainted mine waste unwittingly was used as a garden-soil additive by residents and as fill for the local construction industry.

The government so far has spent $540 million removing more than a million cubic yards of dirt and contaminated building materials from more than 2,000 properties in Libby and Troy.

Just how much remains is uncertain: Agency officials have never fully documented how many homes and businesses were left with vermiculite in their walls after cleanup work was completed.

EPA officials say the towns' health risks have decreased considerably, with airborne asbestos concentrations now comparable to levels in other cities.

For that progress to last, enough money must be available in future years for local officials to provide the proper assistance to homeowners, contractors and others who might encounter vermiculite, said Noble, chairman of an EPA advisory group in Libby.

An EPA research panel concluded last year that breathing in even a tiny amount of asbestos from Libby can scar lungs and cause other health problems.

The agency's proposal includes a number of "institutional controls" to manage the remaining asbestos. They include zoning restrictions that outline which activities are allowed on contaminated property; permit requirements for the disturbance of contaminated soil or building materials; and advisories for firefighters and others who might inadvertently encounter asbestos on the job.

If Tuesday's proposal moves forward following a two-month public comment period, the EPA could wrap most of its Libby work by the end of the decade, officials said.

For now, the Libby area remains in the EPA's Superfund program.

Eventually the community likely will lose that status - and much of the federal funding that goes with it. At that point, oversight for the institutional controls will become the responsibility of local agencies and the state Department of Environmental Quality.

"We know they are going to work only if we can get the community to buy in," the department's Jeni Garcin-Flatow said.