It "won't be a World War III", as the US military is vastly powerful than 10 years ago at the time of the Gulf war, while Iraq's capabilities have declined, he said.

The ground combat the Gulf War lasted just 100 hours

Mr Rumsfeld said he was concerned about possible terrorist attacks sponsored by Iraq.

"I have no doubt that if he's able, he would like to see that terrorist attacks occur in the event that military action was taken."

Mr Rumsfeld was speaking on a call-in radio show broadcast by two American radio stations - National Public Radio and Infinity.

He reminded the audience that the ground combat in the Gulf War, in 1991, had lasted just 100 hours.

"I can't tell you if the use of force in Iraq today would last five days, or five weeks or five months, but it certainly isn't going to last any longer than that," he said.

'Determined'

Mr Rumsfeld insisted that the Iraqi regime has continued its chemical, biological and nuclear weapons programmes and it is prepared to use them.

The United States would do it [the military action] in a manner that would be respectful of human life on all sides but would be determined to do the job and finish it fast

Donald Rumsfeld

Mr Rumsfeld believes the Iraqi leader could launch chemical or biological attacks on US troops as he has done in the past, against Iran and the Kurds.

"One has to be prepared and concerned that could occur," he said.

According to Mr Rumsfeld, if Saddam Hussein had to be ousted by military force, Iraq would be run by a military command until all weapons of mass destruction were tracked down.

Then some sort of interim government would take control of the country.

Mr Rumsfeld said that if the military action becomes necessary, "the United States would do it in a manner that would be respectful of human life on all sides but would be determined to do the job and finish it fast".