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security policy, to be released in the next few weeks, that officials say will result in more documents' being withdrawn. It is asking scientific societies to limit what they publish in research reports.