"The agency's conduct has called into question its ability to investigate public health hazards accurately and appropriately in the future," wrote the chairman and two subcommittee chairmen from the House Committee on Science and Technology in a letter Wednesday to Gerberding.

"Apparently in retaliation, Dr. De Rosa was removed from his post and given a job ... that appears to include no real responsibilities," the letter said.

CDC spokesman Glen Nowak said Friday the agency has not suppressed any science, nor has it retaliated against De Rosa. "The integrity of CDC's science is paramount to everything we do," Nowak said.

De Rosa had been head of the division of toxicology and environmental medicine in CDC's Agency for Toxic Substances and Disease Registry since 1992. He was removed from that job last fall and assigned the title of "special assistant."

Though CDC said De Rosa was simply reassigned, he said in an interview that he's been demoted. De Rosa said the public should be concerned about what's transpired.

"The very people they're looking to for answers have been censored," he said.

At issue is whether the agency intentionally delayed or avoided examining the long-term cancer threat posed by formaldehyde fumes in trailers purchased by the Federal Emergency Management Agency to house victims of the August 2005 hurricane. FEMA initially said air quality in the trailers was safe if they were properly ventilated.

Formaldehyde is a colorless gas with a pungent smell. It is used in the production of plywood and resins. Some studies have linked exposure to formaldehyde with nose and throat cancer.

The committee also is investigating whether CDC abruptly stopped publication of another report involving De Rosa, detailing "disturbing potential health issues" in the Great Lakes region of the U.S., the letter said. The report examined areas with environmental pollution and found elevated levels of certain cancers and other health problems but did not make any cause-and-effect link.

"I want to find out what really happened," said Rep. Brad Miller (D-N.C.), chairman of the Subcommittee on Investigations and Oversight, Friday evening.

It's the latest incident involving allegations that CDC's scientific findings on environmental issues are being watered down.

In October, another committee investigated the White House's involvement in the cutting of nearly seven pages of information about the health consequences of climate change. The deletions were from written testimony Gerberding had planned to give to Congress. Gerberding, however, was adamant she had not been censored.

Nowak said CDC's actions were focused on maintaining high standards of science. He said the Great Lakes report was pulled from publication because parts of it were misleading and didn't meet standards of scientific rigor. The committee is investigating whether agency managers "intentionally circumvented" De Rosa in an initial review of potential dangers associated with the trailers.

FEMA wanted ATSDR to look only at the health effects of short-term formaldehyde exposure -- defined as less than two weeks. Yet many Katrina residents have lived in the trailers for months and years, the committee said in its letter.

De Rosa, the committee's letter said, already had raised questions about the long-term health effects and agency managers knew he would insist the report not be confined to short-term effects. Formaldehyde is a suspected carcinogen that has no safe level set for long-term exposure, the letter said.

"De Rosa was then specifically and consciously excluded in the health assessment," said Miller, referring to information provided to the committee.

Miller said information reviewed by the committee indicates FEMA's requests of CDC were driven by concerns about legal liability, not public health.

FEMA officials declined to be interviewed Friday. But in written statements, they have said the agency didn't ignore, hide or manipulate research. They said the health and safety of hurricane victims was their top priority at all times.

Nowak, the CDC spokesman, said the agency initially focused solely on short-term effects because that's what FEMA asked CDC to look at. But he said the agency later issued a supplemental report with information about long-term health effects.

"Nobody was ignoring the fact that formaldehyde had longer-term health consequences," Nowak said. The agency has been sampling the air quality in more than 500 trailers in Louisiana and Mississippi and is now in the process of analyzing the data.

Congressional investigators, however, said CDC only amended the report to include long-term exposure warnings eight months later -- after De Rosa "persistently demanding" they be included.

De Rosa said Friday that he raised his concerns about formaldehyde, the Great Lakes report and other issues through proper channels within the CDC.

"It's sort of like speaking truth to authority. I knew I was doing it at my peril," he said.

Then, in what investigators said was apparently retaliation, De Rosa was removed from his managerial job and in October given an "unsatisfactory" job performance assessment. Before, De Rosa said, he had received good to excellent ratings.