Anti-US feelings are running high in China

The president is sending three former campaign aides, Deputy Secretary of State Richard Armitage, Deputy White House National Security Adviser Stephen Hadley and Deputy Defense Secretary Paul Wolfowitz overseas to explain US views and seek support.

He has already outlined his plans to the leaders of Britain, Canada, France and Germany and on Tuesday called the Russian president, Vladimir Putin, to reassure him ahead of the speech.

But despite the phone call, Moscow remains apprehensive.

"Many in Washington understand that the destruction of ABM and deploying an anti-missile shield could undermine the system of strategic stability which exists in the world today and lead to a new arms race," the Russian news agency Interval quoted an unnamed "military-diplomatic" source as saying.

Sweden also urged caution.

"We urge President Bush to abstain from the National Missile Defense, just as we urge China, India and Pakistan to discontinue their nuclear arsenals," said Foreign Minister Anna Lindh.

This is one of the biggest turkeys I've seen - there has not been one shred of evidence that it works

Tom Daschle, senate minority leader

Critics have warned that the policy could increase rather than reduce the global risk of accidental attack if it prompts other states to keep large numbers of strategic weapons on hair-trigger alert.

US Democrat Neil Abercrombie, a member of the armed services research and development committee warned that talk of a possible missile defence had spawned "a burgeoning military and corporate apparatus dependent in large measure on missile defense to rationalize its existence."

"Congress must guard against allowing missile defense systems becoming the policy, allowing the technology, in effect, to develop its own psychology."

They need not be 100% perfect in my opinion, and they are certainly unlikely to be in their early stages of evolution

Donald Rumsfeld, US Defence Secretary

Mr Bush also faced criticism closer to home from those who believe that the system does not work and others that the perceived threat can not justify the eventual cost.

Senate minority leader Tom Daschle called the plan "one of the biggest turkeys I've seen... there has not been one shred of evidence that it works," he said, insisting he would demand details on costs and feasibility.

David Wright of the Massachusetts Institute of Technology agreed: "The bottom line is that the technology for the system is not ready," he warned.

Defense Secretary Donald Rumsfeld admitted that the missile defences deployed by the United States were unlikely to be perfect, but would be enough to act as an effective deterrent.

He said: "They need not be 100% perfect in my opinion, and they are certainly unlikely to be in their early stages of evolution."