For two years, Paddleford said, he has been after the U.S. Bureau of Reclamation to give county officials information on the safety of the dam and any potential threats to the structure. Local officials wanted it as part of their emergency planning.

Agency officials maintained the dam, a short distance upstream from the resort community of Jackson, was safe, but Paddleford said they refused to release specifics.

Hearing the speech mentioning the risk to the dam, given by a professor of seismology at the University of California at Santa Barbara, convinced Paddleford that county officials weren't getting the whole story and that the Bureau of Reclamation was being unreasonable.

The dispute highlights a problem faced by some local governments and groups since the terrorist attacks of 2001: It isn't just the general public that is finding it more difficult to get information from state and federal governments about dams, electric utilities or other structures in their areas - whether for safety, environmental or political concerns.

While the Bureau of Reclamation did release what it called a ''nonsensitive'' version of an engineering report, that still did not fully address Paddleford's concerns, he said.

''Everyone knows a dam will fail, but at what point?'' said Paddleford, who was defeated in his bid for re-election last month. ''When should we start looking at evacuating certain areas? When, as a county, do we start looking at those issues?

''I'm accusing no one of wrongdoing, but I want assurances it's safe,'' he said of his seeking an independent review of the report. ''I've gotten, 'The dam is safe,' but to what degree?''

Since the 2001 attacks, government agencies have changed the type of information available for the public and the manner in which it is shared. Some have taken documents or drawings off the Web, while others have changed the classification of some records - marking them as internal, rather than readily available.

In some instances, documents like the full engineering report for the Jackson dam may be reviewed by select officials, who then must sign a nondisclosure agreement.

The dam is an earthen structure with a concrete spillway on the Snake River within Grand Teton National Park. It backs up a lake that, when full, contains about 847,000 acre-feet of water. An acre foot is the amount of water it takes to cover an acre a foot deep.

The dam is about seven miles east of the Teton Fault, which geologists say is overdue for a quake. It could produce a temblor up to 7.5 magnitude, experts say, with ground shaking under the dam that would create forces equivalent to a magnitude 9 earthquake.

Should the dam fail, officials say water would eventually inundate some small towns along the river, including Moran and Wilson. The resort town of Jackson, population about 8,800, sits high enough above the river that officials say it would not be flooded.

Reclamation officials insist there is no significant danger posed by the Jackson Lake Dam. They say they took the unusual step of posting online parts of the highly technical engineering report - also known as a seismic risk analysis - to quell what they see as unfounded fears about the dam's safety.

The Jackson dam report is not alone.

About two years ago, the Federal Energy Regulatory Commission removed from its Web site a document showing that officials had found voids within the aging Milltown Dam on the Clark Fork River, just upstream from Missoula, Mont. County commissioners complained, and an agency official assured the panel it would receive information about the structure.

The local environmental health supervisor said the information had been provided.

Patrice McDermott of the American Library Association said there is growing concern from groups like hers about what she sees as an increase in agencies withholding records as ''sensitive security informa- tion,'' particularly in the past 18 months.

A 2002 Justice Department memorandum suggested to federal agencies that they consider the need to safeguard information ''that could be misused to harm the security of our nation or threaten public safety.''

McDermott contends officials have ''taken the leap from safeguarding information to withholding it. Agencies will err on the side of caution to cover their ass, and we're seeing a rising tide of agencies doing this.''

But agency officials say they're in a difficult position, forced to balance the public's right to know with issues of public safety and security.

Paul Johnston, a spokesman with the U.S. Army Corps of Engineers, said he's unaware of any problems arising from that agency's changes. They have included removing from the Web once readily available information such as engineering drawings, and marking as ''internal'' such information as periodic dam safety in- spections, he said.

Information is shared, though, with appropriate officials, including disaster responders, Johnston said.

The Nuclear Regulatory Commission now is trying to restore some documents to the Web after removing its entire online document library in October for closer scrutiny, spokeswoman Sue Gagner said. Under stricter guidelines, information that ''could be useful or could reasonably be expected to be useful to a terrorist'' may be withheld, she said.

There have been complaints, and Gagner said she's sympathetic. However, ''We've just become more aware of security concerns, as everybody has, since September 11, so we're instituting these reviews.''

States are also aware, and some are taking action. In Wyoming, for example, lawmakers have updated the state's public records act to note exceptions for documents that could, among other things, ''facilitate the planning of a terrorist attack.''