WASHINGTON -- The document seemed innocuous enough: a survey of government data on reservoirs and dams on CD-ROM. But then came last month's federal directive to U.S. libraries: "Destroy the report."

So a Syracuse University library clerk broke the disc into pieces, saving a single shard to prove that the deed was done.

The unusual order from the Government Printing Office reflects one of the hidden casualties of the Sept. 11 terrorist attacks: the public's shrinking access to information that many once took for granted.

Want to find out whether there are any hazardous waste sites near the local day-care center? What safety controls are in place at nuclear power plants? Or how many people are incarcerated in terrorist-related probes?

Since Sept. 11, it has become much harder to get such information from the federal government, a growing number of states and public libraries as heightened concern about national security has often trumped the public's "right to know:"

* At least 15 federal agencies have yanked potentially sensitive information off the Internet, or removed Web sites altogether, for fear that terrorists could exploit the government data. The excised material ranges from information on chemical reactors and risk-management programs to airport data and mapping of oil pipelines.

* Several states have followed the federal government's lead. California, for example, has removed information on dams and aqueducts, state officials said.

* Members of the public who want to use reading rooms at federal agencies such as the Internal Revenue Service must now make an appointment and be escorted by an employee to ensure that information is not misused.

* The Government Printing Office has begun ordering about 1,300 libraries nationwide that serve as federal depositories to destroy government records that federal agencies say could be too sensitive for public consumption.

* Federal agencies are imposing a stricter standard in reviewing hundreds of thousands of Freedom of Information Act requests from the public each year; officials no longer have to show that disclosure would cause "substantial harm" before rejecting a request. Watchdog groups say they have already started to see rejections of requests that likely would have been granted before.

The trend reverses a decades-long shift toward greater public access to information, even highly sensitive documents such as the Pentagon Papers or unconventional manifestos such as "The Anarchist's Cookbook," a compilation of recipes for making bombs. The popularity of the Internet has made sensitive information even easier to come by in recent years, but the events of Sept. 11 are now fueling a new debate in Washington: How much do Americans need to know?

Attacks Place Internet Content in New Light

The swinging of the pendulum away from open records, supporters of the trend say, is a necessary safeguard against terrorists who could use sensitive public information to attack airports, water treatment plants, nuclear reactors and more.

In an Oct. 12 memo announcing the new Freedom of Information Act policies, Atty. Gen. John Ashcroft said that, while "a well-informed citizenry" is essential to government accountability, national security should be a priority.

"The tragic events of Sept. 11 have compelled us to carefully review all of the information we make available to the public over the Internet in a new light," Elaine Stanley, an Environmental Protection Agency official, told a House subcommittee earlier this month.

But academicians, public interest groups, media representatives and others warn of an overreaction.

"Do you pull all the Rand McNally atlases from the libraries? I mean, how far do you go?" asked Julia Wallace, head of the government publications library at the University of Minnesota.

"I'm certainly worried by what I've seen," said Gary Bass, executive director of OMB Watch, a nonprofit group in Washington that monitors the Office of Management and Budget and advocates greater access to government data on environmental and other issues.

"In an open society such as ours, you always run the risk that someone is going to use information in a bad way," Bass said. "You have to take every step to minimize those risks without undermining our democratic principles. You can't just shut down the flow of information."

It's a fine line acknowledged by Stanley. "[The] EPA is aware that we need a balance between protecting sensitive information in the interest of national security and maintaining access to the information that citizens can use to protect their health and the environment in their communities."

The Sept. 11 hijackers, using readily accessible tools like box cutters, the Internet and Boeing flight manuals, hatched a plot too brazen for many to fathom. It forced authorities to consider whether a range of public sites and sensitive facilities was much more vulnerable than they had realized--and whether public records could provide a playbook for targeting them.

Officials acknowledge that there are very few examples of terrorists actually using public records to glean sensitive information, but they say that the terrorist attacks prove the need for extraordinary caution.

The first directive by the Government Printing Office, made last month at the request of the U.S. Geological Survey, ordered libraries to destroy a water resources guide. While documents have been pulled before because they contained mistakes or were outdated, this was the first time in memory that documents were destroyed because of security concerns, said Francis Buckley, superintendent of documents for the printing office.

Because the water survey was published and owned by the U.S. Geological Survey, the libraries that participate in the depository program said they had little choice but to comply. Some librarians asked if they could simply pull the CD from shelves and put it in a secure place, but federal officials told them it had to be destroyed.

"I hate to do it," said Christine Gladish, government information librarian at Cal State Los Angeles, which has pulled the water survey from its collection and is preparing to destroy it. "Libraries don't like to censor information. Freedom of information is a professional tenet."

Peter Graham, university librarian at Syracuse University, said: "Destruction seems to be the least desirable option to me. . . . We're all waiting for the other shoe to drop. Are we going to see a lot more withdrawals [of documents]? That's my fear."

In fact, the Nuclear Regulatory Commission is reviewing publications that it has made available through the Government Printing Office, Buckley said, and it is almost certain to ask for the destruction of some of its titles.

Some have resisted the push to limit access, even on such nerve-rattling subjects as anthrax.

The American Society for Microbiology's Web site--an extensive collection of research articles, news releases and expert testimony--includes information about antibiotic-resistant anthrax. After anthrax-laced letters contaminated the nation's mail system, members of the society debated whether a determined individual could find and misuse the information on its site.

"We . . . decided not to remove it," said Dr. Ronald Atlas, president-elect of the scientific organization. "The principle right now is one of openness in science. . . . If someone wants to publish [a legitimate research paper], we're not going to be the censor."

But that position has drawn scorn from some of Atlas' colleagues.

"We have to get away from the ethos that knowledge is good, knowledge should be publicly available, that information will liberate us," said University of Pennsylvania bioethicist Arthur Caplan. "Information will kill us in the techno-terrorist age, and I think it's nuts to put that stuff on Web sites."

The debate about sensitive information is not a new one. A quarter of a century ago, Princeton University undergraduate John Phillips pointed out the dangers of nuclear weapons when he was able to use publicly available sources to design a crude but functional nuclear bomb.

Phillips, who now heads a political consulting firm in Washington, said in a recent interview that cutting off the flow of information after Sept. 11 is merely a "cosmetic" change when what is really needed are better means of securing access to nuclear and chemical facilities and supplies.

Members of the public will be the ones to suffer, he said. "Restricting information may make us feel good, but terrorists aren't dumb. They'll still be able to get at this information somehow."

In the past, it has taken a tragedy to buck the trend toward more and greater public access. That's what happened in California in 1989 after actress Rebecca Schaeffer was shot to death at her Los Angeles home by an obsessed fan who used publicly available motor vehicle records to find out where she lived. The state quickly cut off public access to such records.

Indeed, chemical and water industry groups are lobbying the Bush administration to curtail regulations providing public access to the operations of public facilities, data that environmentalists say are critical to ensuring safety.

And nongovernment entities such as the Federation of American Scientists have begun curtailing information.

Group Clears Pages From its Web Site

The group recently pulled 200 pages from its Web site with information on nuclear storage facilities and other government sites. For a group known for promoting open information, it was "an awkward decision," concedes Steven Aftergood, director of the federation's government secrecy project.

"But Sept. 11 involved attacks on buildings, and we realized some of the information we had up [on the Web] seemed unnecessarily detailed, including floor plans and certain photographs that didn't seem to add much to public policy debate and conceivably could introduce some new vulnerabilities," he said.

"Everyone is now groping toward a new equilibrium," Aftergood said. "There are obviously competing pressures that cannot easily be reconciled. The critics of disclosure are saying that we are exposing our vulnerabilities to terrorists. The proponents of disclosure say that it's only by identifying our vulnerabilities that we have any hope of correcting them. I suspect that both things are true."