Tony Blair has privately told George Bush that Britain will support an American attack on Iraq if Saddam Hussein refuses to accept resumed UN weapons inspections.

President Bush's "understanding", based on conversations with the prime minister, is that he can count on Mr Blair, according to well-placed Bush administration officials.

The agreement between the leaders comes as diplomatic, military and intelligence sources revealed details of a new plan for the invasion of Iraq, which could take place sooner than had previously been presumed.

The plan involves a slimmed-down force of around 50,000 troops, which could be deployed within a matter of days.

It had been widely assumed that the US could not deploy sufficient numbers of troops needed for the task before the end of this year at the earliest.

Now senior officials are saying a sudden military strike could be launched as soon as October.

Boeing and other US companies are working round the clock, producing satellite-guided "smart" bombs that would be used in huge air strikes to accompany any ground invasion.

Although no plan of attack has yet been finalized, Mr Blair has already offered "in principle" to lend full British military and diplomatic backing for an assault.

Mr Blair insists in public that no decision has been made about British involvement in any US military attack on Iraq. "We are not at the point of decision yet," he told a Downing Street press conference on Thursday.

A Washington source familiar with administration thinking said that while it was accurate to say Mr Bush had not yet decided how or when to attack Iraq, the president was considering his options in the belief Mr Blair would go along with the US.

Two options have been widely discussed in Washington. One would involve inserting Iraqi defectors, backed by 5,000 US troops and "precision" air strikes. The plan was once dismissed by General Anthony Zinni, America's Middle East envoy, as a recipe for a "Bay of Goats" disaster, comparable to the 1961 Bay of Pigs fiasco in Cuba.

The second option, which would require at least a three-month build-up, is the US military's central command standard war plan, involving 250,000 troops and heavy armour. Britain, it is suggested, would contribute 30,000 troops, an armored division backed up by air and sea support.

A new third option now being considered is for a sudden strike, involving no more than 50,000 troops who would bypass the Iraqi army and make straight for Baghdad.

With thousands of US troops already deployed in Kuwait and Qatar, such a plan could be executed quickly, officials say.

Though a sudden attack combining air power and ground forces would still involve huge risks, it would have the advantage of avoiding mounting opposition to military action against Iraq in such countries as Saudi Arabia and Jordan - whose bases the US might not need - as well as wrongfooting Saddam Hussein, officials say.

British military sources describe this third option as "high risk" but with a "high payoff" were it to succeed.

The US officials say Mr Bush has also obtained agreement in principle for support from France in conversations with President Jacques Chirac.

Mr Blair is understood to have told Mr Bush that British support is contingent on the completion of a genuine effort to persuade Iraq to readmit weapons inspectors.

Mr Blair has also insisted that Mr Bush offer a "full explanation" in public of his reasons for going to war and that a "major effort" be made to win over skeptical public opinion. "Blair wants him to make the case," a source said.

Part of the Blair-Bush understanding was that evidence that Iraq presented an urgent threat through its alleged attempts to obtain weapons of mass destruction would be published in London.

The source said Britain and the US were jointly opposed to seeking a new UN security council resolution to justify an attack on Iraq. Both countries will adopt the position that action is allowable under existing UN resolutions.

Mr Blair indicated on Thursday that the weapons inspections talks, which Kofi Annan, the UN secretary general, has suspended indefinitely after an unsuccessful Vienna meeting this month, would fail - thus increasing the likelihood of an attack.

© Guardian Newspapers Limited 2002

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