SALT LAKE CITY -- Despite opposition from two states' congressional delegations, Pentagon officials say they will continue to consider shipping chemical weapons from Colorado to Utah for disposal.

Senators from Colorado and Utah told the Salt Lake Tribune's Washington office Monday that studying the possibility is a waste of time and money because shipping the weapons is illegal under U.S. law.

"These chemical munitions are not going to be transported, one, because it's a violation of federal law and, two, because of community concerns with public safety," said Sen. Ken Salazar, D-Colo.

But Congress should understand all options, Undersecretary of Defense Michael Wynne said.

The international treaty known as the Chemical Weapons Convention sets 2012 as the deadline for the disposal of weapons stockpiles, and moving them might be the only way to meet it, Wynne suggested.

He said other options were changing federal law or violating the treaty.

"If you really wanted to comply with the chemical weapons treaty you would accommodate some of the options we're considering, such as transportation," Wynne said.

Last week, the Senate Appropriations committee used an emergency spending bill to try to block the Pentagon's study.

Department of Defense officials want to look at shipping mustard gas munitions stored at a Pueblo, Colo., depot to incinerators around the country, including the Tooele Army Depot about 45 miles southwest of Salt Lake City.

Federal law prohibits shipping chemical weapons across state lines.

Wynne argues, however, that mustard gas would be relatively safe if shipped in winter, when cold temperatures stabilize the volatile agent.

Before incineration began in 1996, Utah once housed about 40 percent of the nation's chemical stockpile.

That's already "more than enough," Sen. Bob Bennett, R-Utah, said last week after the appropriations vote to block funding for the Pentagon study.

The full Senate is scheduled to debate the spending bill this week.

But the study is scheduled to be complete by April 30 and could be finished before Congress enacts legislation to prohibit it.

Sen. Wayne Allard, R-Colo., said the Defense Department needs to stop studying the issue at some point and take action to meet the treaty deadline.