The Bush administration is taking wide measures to tighten scientific secrecy in the hope of keeping weapons of mass destruction out of unfriendly hands.
Last month, it began quietly withdrawing from public release more than 6,600 technical documents that deal mainly with the production of germ and chemical weapons.
It is also drafting a new information security policy, to be released in the next few weeks, that officials say will result in withdrawing more documents.
In addition, it is asking scientific societies to limit what they publish in research reports.
"We're working hard for a set of guidelines so terrorists can't use information that this country produces against us," Tom Ridge, the director of homeland security, said in an interview.
He added that scientists were being closely consulted on new guidelines.
But critics say the most extreme steps proposed could make it impossible for scientists to assess and replicate the work of their colleagues, eroding the foundations of American science. They fear that government officials eager for the protections of secrecy will overlook how open research on dangerous substances can produce a wealth of cures, disease antidotes and surprise discoveries.
"It comes down to a risk-benefit ratio," said Robert R. Rich, president of the Federation of American Societies for Experimental Biology. "I think the risk of forgone advances is much greater than the information getting into the wrong hands."
One White House proposal is to eliminate the sections of articles that give details that researchers from other labs would need to replicate the claimed results, helping to prove their validity.
"That takes apart the whole foundation of science," Ronald M. Atlas, president-elect of the American Society of Microbiology, said of omitting methods. "I've made it reasonably clear that we would object to anything that smacked of censorship. They're discussing it, and I wouldn't rule out them doing something."
Abigail Salyers, the society's president, offered a more pointed rebuff. "Terrorism feeds on fear, and fear feeds on ignorance," she said in a statement to appear in the March issue of the group's magazine.
The best defense against anthrax or any infectious disease, Salyers added, is information that can bolster public safety.
Ridge said the critics were overreacting. "I can understand their concern, but I'm not sure the alarm bells should be rung just yet," he said.
"Let's first do the work" of producing the new guidelines, Ridge said. He added that the scientists "have to remember what we're up against": terrorism with exotic weapons that could maim or kill millions of people.