WASHINGTON, April 24, 2005 -- Federal agencies under the Bush administration are sweeping vast amounts of public information behind a curtain of secrecy in the name of fighting terrorism, using 50 to 60 loosely defined security designations that can be imposed by officials as low-ranking as government clerks.

No one is tracking the amount of unclassified information that is no longer accessible.

For years, a citizen who wanted to know the name and phone number of a Pentagon official could buy a copy of the Defense Department directory at a government printing office. But since 2001, the directory has been stamped ''For Official Use Only," meaning the public may not have access to such basic information about the vast military bureaucracy.

After a 1984 chemical plant accident killed 20,000 people in Bhopal, India, Congress in 1986 passed the Emergency Planning & Community Right to Know Act, giving Americans the right to know if they lived downwind from dangerous chemicals. Until 2001, the Environmental Protection Agency posted on its website each plant's plans for dealing with a disaster, leading to public pressure on the chemical industry to maintain safer conditions. The database has been removed from the website for security reasons.

For decades, the Defense Department's map office has made its topographic charts available to the public. Biologists use them to map species distribution, and airlines use them to create flight charts. But the administration has proposed removing the maps from public use this fall, in part to keep them away from ''those intending harm" to the United States.

In these cases and others, the information that the Bush administration is removing from public access is not risky enough to national security to be officially classified as ''Confidential," ''Secret," or ''Top Secret," under rules in place for decades.

The public instead is losing access to large amounts of less-risky information through terms such as ''For Official Use Only," ''Sensitive But Unclassified," ''Not for Public Dissemination," and what Congress has estimated as 50 to 60 other designations developed by federal agencies to keep the public from seeing unclassified information.

Although some of these secrecy terms predate the Bush administration, advocates of open government say their use has grown sharply over the past four years. Precise numbers of documents being shielded are unknown because the administration keeps no records. And there are only vague standards governing the types of documents that can be made secret.

Under the official system for classified secrets, for example, each level of secrecy comes with clearly defined criteria. There are strict limitations on who is authorized to decide whether a piece of information should be classified. Precisely 4,007 officials have this power. There are time limits after which most classified secrets can become public. There is a process for appealing a classification. And the government tracks how many classified secrets it creates each year.

By contrast, terms such as ''For Official Use Only" have vague criteria that vary from agency to agency. In some departments, any employee, even a clerk, may stamp a document as off-limits. All 180,000 employees of the Homeland Security Department may decide a document is ''For Official Use Only."

There is no system for tracking who stamped it, for what reason, and how long it should stay secret. There is no process for appealing a secrecy decision.

''Information is getting withheld arbitrarily and unnecessarily," said Steven Aftergood of the Federation of American Scientists' Project on Government Secrecy. ''That is bad because it impedes oversight and obstructs accountability. It is the nature of bureaucracies to hoard information, and these new unclassified control mechanisms allow them to do that without restraint."

Asked about government secrecy at a recent conference of newspaper editors, President Bush said he felt that ''citizens ought to know as much as possible about the government decision-making." But he also warned that the country had to be careful about information that could put lives at risk.

''I understand that there's a suspicion that we're too security-conscious," Bush said. ''I hope that we're becoming balanced between that which the public ought to know and that which, if we were to expose, would jeopardize our capacity to do our job, which is to defend America."

But critics contend that the system is far from balanced because the standards for sensitive but unclassified information are so loose. In some cases, the administration appears to have shielded information that posed no realistic security risk, but did threaten its political interests. Other times, bureaucrats appear to have acted overzealously, blocking useful information to no end.

Representative Henry Waxman, Democrat of California, identified a series of incidents in which he said security controls were invoked improperly to prevent political embarrassment.

For example, in the midst of the 2004 presidential campaign, the State Department released a report showing that during the Bush administration terrorist attacks around the world had dropped to their lowest levels since 1969. But after critics challenged the numbers, the department recalibrated and found that attacks were, in fact, at a 20-year high.

That September, just weeks before the election, the department's inspector general completed a report blaming CIA analysts for producing faulty numbers. The administration withheld the report from the public as ''Sensitive But Unclassified."

Now, the State Department has decided not to tabulate attacks in the annual terrorism report. Larry C. Johnson, a former CIA and State Department terrorism specialist, contended that the decision occurred after early results showed that attacks jumped again, undercutting Bush's claim to be winning the war on terrorism.

Said Waxman: ''It is indefensible to conceal the terrorism numbers from Congress and the public."

Hammered by criticism after Johnson's allegations, State Department spokesman Richard Boucher last week denied that the decision to stop tabulating attacks was political. Boucher said the new National Counterterrorism Center would handle any public dissemination of statistics, though he was unable to say when it would provide the official 2004 numbers.

In another recent case, Human Rights Watch earlier this month found an unclassified draft of a new policy on a Defense Department website. The document proposed holding suspected Iraqi insurgents without trial in the same way that accused Taliban members have been imprisoned at Guantanamo Bay.

After Human Rights Watch denounced the idea, the Pentagon took down its entire electronic library of unclassified documents, including many hundreds of unrelated papers. The military later put part of the website back up, but dozens of unrelated documents that were previously available to the public are still gone.

Such secrecy moves have been criticized across the political spectrum. A recent report coauthored by the Heritage Foundation, a conservative think tank, attacked ''overzealous" decisions to dismantle entire websites over security fears.

It also said that the Bush administration has not conducted a systematic review of formerly public information that has been made secret, by weighing the likelihood that it could help terrorists against the ''countervailing public safety and other benefits of providing" the information.

The move toward withholding unclassified information from the public occurs as the administration's use of the classified secrets system is soaring. It classified 16 million documents in 2004, the highest number recorded since the government began keeping track of them in 1980. That number is up from 14 million in 2003, 11 million in 2002, and 8 million in 2001.

And the number of old documents being declassified dropped from an average of 150 million a year during Bill Clinton's second term to an average of 54 million in Bush's first term. Last year, there were only 25 million declassifications.

Although no numbers exist to track the number of unclassified documents withheld from public view using a bureaucratic term such as ''For Official Use Only" or by dismantling a website, anecdotal examples are mounting.

Last month, Representative Edward J. Markey, Democrat of Malden, asked the inspector general of the Nuclear Regulatory Commission to examine whether the agency was using security threats as a ''pretext to prevent the public from accessing documents that do not pose a security risk." The inspector general agreed last week to launch an investigation.

Markey contended that the commission had blocked the public from viewing unclassified nuclear information, so that only members of the industry were able to discuss regulatory changes with the government. For example, the NRC recently withheld a National Academy of Sciences report challenging the idea that the industry-preferred way of storing spent nuclear fuel rods was safe from terrorism, prompting Markey to accuse the agency of suppressing information ''based on the fact that it disagrees with the conclusions, not on any legitimate security" fears.

Meanwhile, Wenonah Hauter of Public Citizen has also raised concerns about the NRC's proposal to prevent outside groups from viewing unclassified safety plans. Public-interest groups have used such information to pressure the agency to adopt higher standards for nuclear security, including protecting power plants from truck bombs. If the proposed changes go through, the public would be left ''in the dark about the competency of the nuclear industry," Hauter said.

Sue Gagner, a spokeswoman for the NRC, said the agency is ''very mindful of the public's need to know," but its ''concern is not to release information that could be helpful to a terrorist."

With a few exceptions, the terms such as ''For Official Use Only" lack the force of law, so if a member of the public finds out that the document exists, he or she may still try to obtain it under the Freedom of Information Act. However, the Bush administration is also fighting to avoid releasing information under the act.

Under a Clinton administration policy, FOIA officers were supposed to operate with a ''presumption of disclosure" unless it was ''reasonably foreseeable that disclosure would be harmful."

But in October 2001, then-Attorney General John Ashcroft reversed course, instructing agencies to withhold information unless there was no ''sound legal basis" for doing so.

This policy discourages the release of information because few people are willing to go to the trouble of filing a lawsuit. The administration has also stretched the legal definitions of what is exempt, making FOIA exceptions for documents that would invade personal privacy or reveal internal agency procedures apply more sweepingly.

For example, Forbes Magazine reported in July 2004 that the Justice Department cited ''unwarranted invasion of personal privacy" in rejecting an FOIA request for press releases it had already issued concerning terrorism-related indictments.

''If you can control the flow of information, you often can control the process itself," said Peter Weitzel of the Coalition of Journalists for Open Government. ''I think they believe that's the most effective way to govern, and so that's what they sought out to do."

Some Republicans also worry that the government is being too secretive. Two Texas Republicans, Senator John Cornyn and Representative Lamar Smith, have sponsored a bill to strengthen the Freedom of Information Act by closing loopholes, speeding up responses to FOIA requests, and establishing an FOIA hotline service, among other things. ''Achieving the true consent of the governed requires informed consent, and such consent is possible only with an open and accessible government," Cornyn said in February.

Cornyn, a former Texas attorney general, said the federal government often places documents beyond public view ''without real justification." He called for a system that ''strikes the right balance between the need to classify documents in our national interest and security, and our national values of open government."

Bryan Bender of the Globe staff contributed to this report.
© Copyright 2005 The New York Times Company