The Army's disclosure came only a day after Defense Department officials assured Colorado's two U.S. senators that a planned $1.6 billion plant would be built in Pueblo to destroy the 780,000 chemical munitions stored there.

Michael Parker, director of the Army's Chemical Materials Agency, said in a statement Wednesday that his office had been told by the Defense Department to begin a study "that considers and evaluates relocation of some of the chemical weapons stockpile."

Plans to get rid of the Pueblo Chemical Depot's mortar rounds and artillery shells filled with mustard gas have been in the works for at least 19 years. The work would bring 1,000 jobs to Pueblo.

This month, a citizens' watchdog group expressed concerns that the Pentagon was cutting construction money for the Pueblo plant and one in Blue Grass, Ky., and was studying plans to transport the weapons to other destruction sites.

A treaty requires the United States to destroy all of its chemical weapons by 2012.

Of the eight U.S. chemical weapons sites, only Pueblo and Blue Grass do not have incinerators or water-based neutralization plants already operating or nearing completion.

Concerned about the possible delay in Pueblo, Colorado Sens. Wayne Allard, a Republican, and Democrat Ken Salazar met with Deputy Assistant Defense Secretary Patrick Wakefield on Tuesday.

After that meeting, the senators said they were assured that the Pueblo plant would go forward, although there would be a delay because of funding cuts.

But Wakefield himself had written a memo Jan. 10 telling the Army to address methods of "safeguarding the chemical weapons stockpile when relocation among its sites is considered as one of these alternatives" to meeting the 2012 treaty.

The memo was released by the Chemical Weapons Working Group, a national organization that has supported water-neutralization of the chemical weapons and opposed the Army's original plan to burn them.

Allard's office remained adamant that the Army would not be allowed to transfer weapons from Pueblo.

"It's not going to happen," said Angela de Rocha, Allard's press secretary.

"Study or no study, the stuff is not going to be moved. That is what the senators were told unequivocally on Tuesday, that it's not a viable option to move it," she said.

Federal law currently forbids transporting chemical weapons from their depot sites. State regulations also prohibit their removal.

Opponents say transporting the materials from their depot sites could endanger lives by exposing the weapons to accidents on roads or terrorist attacks.