Whistle-blowers, members of Congress and interest groups have for several years attacked the agency, saying it has been weakened by industry and political influence at the expense of sound science and public health.

In the questionnaire, 15% of the 997 FDA scientists who responded said they had been asked to "inappropriately" exclude or alter information or conclusions in agency documents for nonscientific reasons. Thirty-two percent said the FDA didn't routinely provide complete and accurate information to the public. And 37% said FDA leaders weren't as committed to product safety as to approving products for sale.

FDA spokeswoman Susan Bro sharply disputed the findings, criticizing the "unscientific rigor" of the survey and stressing that the agency was committed to protecting the public health.

"This is a counterproductive exercise based on leading questions and innuendo," Bro said.

But congressional critics of the FDA said the survey provided further evidence that the agency's mission of ensuring the safety of drugs and medical devices had been lost.

Senate Finance Committee Chairman Charles E. Grassley (R-Iowa), who has led a hearing into safety issues with the painkiller Vioxx and is leading an investigation of the antibiotic Ketek, called in a statement for a "major overhaul and a culture change at the highest levels" of the FDA.

The agency, Grassley said, "needs to reestablish its relationship with its own scientists and distance itself from the drug industry. The FDA needs to get rid of its mind-set that it's a facilitator for the drug industry and become regulator once again. The FDA's focus should be only on science and the public good."

The Union of Concerned Scientists is a nonpartisan group that has been critical of the Bush administration's treatment of government scientists.

Its survey was mailed to 5,918 scientists.