Ashcroft did not say if the threat was made against a specific natural gas pipeline, storage site or liquefied natural gas (LNG) plant.

The administration is worried that attacks on the United States might resume if Saudi-born militant Osama bin Laden, who Washington believes was the mastermind behind the Sept. 11 attacks on New York and Washington, is captured or killed.

"We're especially always concerned as it relates to things that might have substantial hazard, and some of our energy (facilities) have substantial hazard," Ashcroft said.

Energy industry trade groups were notified of the threat, he said.

Justice Department spokeswoman Mindy Tucker said FBI headquarters told its field offices on Nov. 17 about possible plans to attack natural gas supplies, based on the death or capture of bin Laden or Taliban leader Mullah Mohammad Omar.

She emphasized the information was "uncorroborated" and from "a source of questionable reliability." Tucker told reporters the warning was one of dozens that the FBI has issued since Sept. 11.

The American Petroleum Institute and American Gas Association were among the energy trade groups that received the FBI warning last Tuesday.

"We have received uncorroborated information that Osama bin Laden may have approved plans to attack natural gas supplies in the United States," said the FBI warning.

"We have no additional details on how such an attack would be carried out or which facilities would be targeted," the FBI added.

The energy groups forwarded the government warning verbatim to their member companies.

Officials with both groups said their member firms were already on high alert for sabotage and there were few additional security measures the companies could take.

MOST NATGAS PIPELINES UNDERGROUND

Natural gas is delivered domestically through a two-million-mile pipeline system, most of which is underground, according to the American Gas Association.

Because the delivery system is so vast, sabotage on a particular pipeline would not result in any long-term supply disruption, according to experts. Also an explosion along a pipeline segment could be controlled with safety valves that could cut off natural gas feeding a fire.

Natural gas provides about 24 percent of all the energy used in the United States, or one-third of the energy if transportation fuels are excluded, the trade group said.

Ashcroft's comments come as federal energy regulators take a second look at the planned reopening and expansion of the Cove Point LNG plant near the Calvert Cliffs nuclear power plant located on the Chesapeake Bay in southern Maryland.

The Federal Energy Regulatory Commission, which approved the Williams Cos. project last month, is now considering the national security implications of having huge LNG tankers unload at a facility just a few miles down the road from Constellation Energy Group's Calvert Cliffs nuclear plant.

An LNG facility in Boston had been closed by state officials following the Sept. 11 attacks on the World Trade Center and the Pentagon. Officials feared an LNG tanker entering Boston harbor could be subject to sabotage, causing massive damage.

Maryland Democratic Sen. Barbara Mikulski has demanded that FERC rescind its operating certificate for the Cove Point plant, warning the facility is a terrorist target.

"This is especially true as Attorney General John Ashcroft today announced possible threats to the American natural gas sector," she said this week.