Despite a large Pentagon buildup in the Gulf region, the use of force against Iraq is possible but not inevitable, US Defence Secretary Donald Rumsfeld has said.

"The first choice would be that Saddam Hussein would pack up and leave the country tonight. That would be nice for everybody. Or he would decide suddenly to turn over a new leaf and cooperate with the UN and disgorge all his capabilities. These are terribly dangerous weapons -- chemical weapons and biological weapons," he told reporters.

He said President George W Bush had not yet decided to use force against Iraq, but the continuing flow of American troops to the region will give him greater flexibility in dealing with the Iraqi president.

The defence secretary would not say how large a force the Pentagon was assembling in the Gulf region or provide details on military units slated for deployment.