The Pentagon's top military official says Friday the United States has evidence Baghdad may be using mobile laboratories to make chemical or biological weapons. The White House is expected to soon begin laying out its case that Iraq poses a level of danger that could require military action to stop.

This is the first time the Bush administration has said unequivocally that Iraq has mobile weapons laboratories, and may be using them to rebuild the kinds of weapons it agreed to give up at the end of the Gulf War 11 years ago.

A day after President Bush warned the world the United Nations must act against Baghdad, Joint Chiefs of Staff Chairman General Richard Myers appeared to make the case that it would be worthless for the U.N. to send weapons inspectors back to Iraq. He told reporters at the National Press Club Saddam Hussein has mobile laboratories that could easily be hidden from them.

"It does not take a lot of space for some of this work to go on. It can be done in a very, very small location," he said. "The fact that you can put it on wheels makes it a lot easier to hide from people who might be looking for it. So, yes we have evidence."

Iraq denies it still has such weapons and is refusing to allow U.N. inspectors to return anyway. But General Myers' comments mark the start of what is expected to be an administration effort to make its case about the dangers that Iraq's alleged attempts to rearm poses to the world.