About 180 people who were diagnosed with asbestos-related illnesses linked to W.R. Grace & Co.'s now-defunct mine in Libby, Mont., were misdiagnosed, the Columbia-based specialty chemical maker asserted in a statement yesterday.

The finding is based on an audit by Grace's health care administrator in Libby, which had a panel of board certified chest radiologists review the X-rays and CT scans of Libby residents admitted to the plan because local physicians determined they were sickened by asbestos from the Libby mine.

In a letter to these participants, the health plan administrator, HNA/Triveris, assured them that they are entitled to keep the "core benefits" even if they do not have asbestos-related diseases. Those benefits include annual exams, chest X-rays, flu shots, gym memberships, inhalers and even hospice care "regardless of the condition necessitating such care."

But participants in the plan who are deemed to have asbestos-related disease are entitled to broader benefits, including "any care that's appropriate for an asbestos-related condition," according to a person familiar with the plan who spoke only on the condition that he not be named because of pending legal proceedings. Those who received the letter from Grace would not be entitled to treatment beyond the core benefits, even for some symptoms similar to those caused by asbestos.

The letters triggered an angry response on Capitol Hill, where Montana lawmakers accused the company of shirking the commitment it made to provide medical care for Libby-area residents.

Earlier this week, Sen. Max Baucus (D-Mont.) introduced legislation that would force Grace, now under bankruptcy court protection, to create a $250 million health care trust fund for Libby's asbestos victims before it emerges from bankruptcy proceedings. "We've always feared Grace would bail out of their health care responsibilities," Baucus said in a statement. "That's why we must continue to hold Grace's feet to the fire in every way we can."

Rep. Dennis Rehberg (R-Mont.) asked the U.S. Department of Health and Human Services to investigate the decision by HNA/Triveris, which began administering the plan in 2000 shortly after news reports linked deaths in Libby to the Grace mine.

Grace said it will cooperate fully with an investigation.

Grace's ties to Libby date back to 1963, when the company purchased a mine that contained abundant deposits of vermiculite, a mineral used in fireproofing spray, potting soil and attic insulation. The vermiculite contained naturally occurring asbestos that infused the air of the Libby mine, blew into the town and was carried home by workers, the company and the residents agree.

In February, federal prosecutors charged Grace with burying a paper trail dating to 1976 that demonstrated the exposure of Libby residents to asbestos. They said the death rate from asbestos is now 40 to 80 times as high in Libby and surrounding areas as elsewhere in the country and that 1,200 area residents have lung abnormalities linked to the asbestos exposure.

Grace denies criminal wrongdoing and says it took steps to reduce asbestos exposure as knowledge about the danger emerged.