Mr Rumsfeld wants to review the US military's priorities in Asia

But the talks, aimed at giving US troops more flexibility to react to new threats like terrorism, are likely to be overshadowed by security in Iraq.

On Thursday, Japan postponed sending troops to Iraq after a suicide bombing on an Italian police station killed 27.

Mr Rumsfeld, on his first east Asian tour since becoming Defence Secretary in 2001, goes to South Korea on Sunday.

The importance of this region really can't be overstated Donald Rumsfeld US Defence Secretary

On his way to Japan, Mr Rumsfeld stopped on the Pacific island of Guam, a US dependant territory.

"The importance of this region really can't be overstated," he told American forces there.

He said the US Defence Department was likely to announce changes to the make-up and basing of some of its overseas forces by the end of the year.

Plans are likely to include changes to the 37,000 US troops currently in South Korea, and the 50,000 stationed in Japan.

Mr Rumsfeld has said he wants to move away from an era of "static defence" to make US forces more flexible in dealing with new security threats like terrorism.

"That requires more agility, it requires access to a larger number of locations," he told reporters after he left Washington.

Media reports said the US marines currently stationed on the Japanese island of Okinawa might be withdrawn.

And a change in the deployment of US troops in South Korea is already under discussion.

Among the proposals is that they withdraw further south, away from the range of North Korean artillery.

It is also possible that their numbers will be reduced.

Public opinion

Mr Rumsfeld is expected to discuss the North Korean nuclear stand-off, as well as the situation in Iraq.

Japanese Prime Minister Junichiro Koizumi, a staunch supporter of the US-led occupation in Iraq, received parliamentary approval last July to send up to 1,000 troops there.

But BBC Tokyo correspondent Jonathan Head says that since then, as the security situation has deteriorated, an already uneasy Japanese public has turned against the policy.

It is thought Mr Rumsfeld is unlikely to put any pressure on Mr Koizumi for fear of aggravating his difficulties.

The proposed area of deployment for the Japanese troops was Nasiriya, the scene of Wednesday's bombing on the Italian police station which killed 27 people.

South Korea is also showing reluctance to become overly involved there.

Washington asked Seoul for 5,000 soldiers on top of the 400 non-combatants it already has in Iraq.