WASHINGTON (AP) _ The White House has ordered government agencies to remove from Web sites and public documents any sensitive information, such as locations of nuclear materials, that might help terrorists.

White House Chief of Staff Andrew Card sent a memo to the heads of all agencies and executive departments on Wednesday directing them to immediately safeguard any government records that could help terrorists.

Card also ordered them to take a look at all public documents and report back to the Office of Homeland Security within 90 days.

``This is very serious business,'' White House spokesman Ari Fleischer said. ``People inadvertently had information pre-September 11 that should be viewed in a different context in the post-September 11 era.''

Card's memo, first reported by The Washington Times, told officials to protect information on weapons of mass destruction ``including information about the current locations of stockpiles of nuclear materials that could be exploited for use in such weapons.''

``You and your department or agency have an obligation to safeguard government records,'' Card wrote.

The information in question includes non-classified information available to the public for years.

Steven Aftergood, who directs a government secrecy project at the Federation of American Scientists, said one ``potentially troublesome feature'' of the order is that the material to be reviewed includes ``Sensitive But Unclassified Information.''

``The need to protect such sensitive information from inappropriate disclosure should be carefully considered, on a case-by-case basis, together with the benefits that result from the open and efficient exchange of scientific, technical, and like information,'' according to a more-detailed memo about the directive written by the administration's Information Security Oversight Office.

But no detailed criteria for conducting such case-by-case consideration was provided, leaving this category seemingly open-ended, Aftergood said.

Fleischer acknowledged that the changes would make things more difficult for people who want the information for legitimate purposes, but said the seriousness of the threat requires caution.

``Our enemies are people who have shown an ability and a desire to use our technology against ourselves,'' Fleischer said.