By William Horsley BBC European Affairs correspondent

Tony Blair has boldly defended US policy, President George W Bush, and his threats of military action to topple the regime of Saddam Hussein in Iraq.

He says Britain will not leave America to face the "unique" threat from Iraq alone.

He claims to be a bridge between Europe and America at a time of deep splits. He calls Britain a leading partner in Europe. And he wants the European Union to be "a superpower".

All these claims are about to be put to the test. Mr Blair is playing for high stakes.

The odds are stacked against him as he seeks to turn the tide of public opinion in Europe, and keep Europe from breaking ranks with the US.

He brushes aside the polls showing public opinion in Britain now opposing a war against Iraq. His message is: "When people see the evidence they will understand that we must act".

He is to publish the evidence on the threat of Saddam's weapons of mass destruction within weeks.

Challenge

Mr Blair is taking on all comers in the anti-war faction - the Archbishop of Canterbury, the trade unions, many Labour MPs and several members of his own cabinet.

Bush is set to talk to Blair at the weekend

His task in Europe is greater still.

German Chancellor Gerhard Schroeder is campaigning for re-election on the plank of opposition to war with Iraq. He says military action now would be "without German support".

Even conservative would-be Chancellor Edmund Stoiber says he would deny the US the use of German troops and equipment.

In France President Chirac says "the UN must decide" on matters of war and peace.

Nelson Mandela, the world's elder statesman, says he is "appalled" that the US is talking of attacking another country without the backing of the UN.

Plan

Tony Blair and his government think they have an answer to all this.

It is a plan in 3 parts:

• Take the issue back to the United Nations. Mr Blair says the UN Security Council may be asked to authorise military action. But if it fails to make Iraq comply with its resolutions within 2 or 3 months, a war could follow "with the widest possible international support".

• Line up the Europeans behind a "road map" which combines diplomacy with the threat of war. Last weekend EU foreign ministers, meeting in Denmark, informally agreed on this approach.

• Answer the fears of pro-western Arab states. Tony Blair says there must be a settlement in the Middle East which is "just and fair" to the Palestinians. And he highlighted the fact that Saddam Hussein has killed large numbers of his own people with chemical weapons which he could also use against others.

Tony Blair seems to be going against the tide of world opinion.

He acknowledges the risk of Iraqi retaliation. But he believes there is no alternative to taking action in the face of the threat. In Kosovo and Afghanistan he said the same.

With the US and Britain acting together, and Britain helping to keep Europe on side, Mr Blair believes he can defy the odds and win.