By Greg Barrow BBC UN Correspondent

The fate of Iraq could provide a defining moment for the United Nations, more than half-a-century after the organisation was created in the aftermath of the Second World War.

This time, it is the prospect of a war to remove Iraqi President Saddam Hussein that may decide the importance of the UN's role in the 21st century.

What sort of Iraq do we wake up to after the bombing, and what happens in the region

Kofi Annan

If global action against Iraq is decided in the form of UN Security Council resolutions, then the organisation can claim, once again, to be driving international diplomacy.

On the other hand, the UN could be dealt a mortal blow if the world's only superpower, the United States, decides to go it alone, bypassing the UN and pursuing regime change in Baghdad unilaterally.

Diplomats are waiting anxiously to hear what President Bush has to say when he speaks to the UN General Assembly in New York on Thursday.

War drums

The audience at UN headquarters, as well as around the world, will hang on every one of President Bush's words.

President Bush will address the UN General Assembly

His speech is likely to say as much about the future of Iraq and its leader, Saddam Hussein, as it will about the UN and its role in the aftermath of last year's attacks on the United States.

UN Secretary General Kofi Annan has tried to maintain a calming presence as the drums of war have been beating more loudly.

On his return to UN headquarters in New York this week, he urged world leaders to carefully consider the consequences of war in Iraq.

"What sort of Iraq do we wake up to after the bombing, and what happens in the region?" he asked.

"What impact would it have? These are questions leaders I have spoken to have posed."

First step

Mr Annan also asked the Security Council to make its views known on this issue.

Despite the intensity of the rhetoric emanating from Washington, the council has so far avoided any direct engagement in the issue of Iraq.

Kofi Annan wants a meaningful debate

That could soon change, as European leaders have been keen to persuade the Bush administration that a new resolution on Iraq is the best first step towards resolving the Iraqi question.

Although Washington regards regime change in Baghdad as the only way forward, many nations still want to pursue the goal of getting UN weapons inspectors back into Iraq after an absence of almost four years.

The problem is how to persuade the Iraqis that this is in their national interest, at a time when the United States has intimated that it will still push on to pursue its military objectives against Saddam Hussein, whether UN weapons inspectors are allowed back or not.