By Tom Carver BBC Washington correspondent

What does the US really want out of a war with Iraq?

Some would say oil. The Middle East has 65% of the world's oil reserves. The US consumes 30% of the world's oil.

The US wants to see the Middle East more democratised

People see George Bush, the one time owner of a (rather unsuccessful) oil company and his oil friends like Dick Cheney and Don Evans and assume that they personally want to take control of the Middle East's supplies of oil by force.

But if you want to understand what motivates these men, you must look beyond these phrases.

For better or worse, oil is the lifeblood of the American economy and the US certainly believes it must keep the flow of oil going.

But it is not intending to do it by military occupation. Long-term military domination (apart from being unrealistic) is a very inefficient and extremely costly method of getting your way.

Changing priorities

In the last Gulf War, stability was the top priority for George Bush senior.

He set a limited military objective of pushing Saddam out of Kuwait and at the urging of the other Arab regimes, he agreed not to rock the boat by driving on to Baghdad and overthrowing him.

All that changed on 11 September. This George Bush is no longer willing to let weapons of mass destruction remain in the middle of such a volatile region.

And he is no longer willing to let a man who has used those weapons against his own people and others remain in power.

This is a fundamental difference between Bush and his father.

Bush Jnr (left), unlike his father, will not allow the Iraqi leader to retain power

It does not matter to this White House that they haven't uncovered a conclusive link between Saddam and al-Qaeda.

It does not matter to them whether or not the inspectors find a "smoking gun".

This administration believes that, in this new world, it can not risk letting a man like Saddam remain in power, in that part of the world, with these kind of weapons.

But their agenda extends beyond Saddam. What America wants is a more democratised Middle East as a bulwark against the spread of fundamentalism.

It believes that inserting a democratic, western-leaning government in Iraq will encourage others in the region to democratise.

'March of democracy'

The not-so-subtle subtext to an invasion of Iraq is to send a serious shiver down the spine of every Arab ruler:

The US wants to deny Islamic militants access to oil reserves

"We are watching you. We want you to get your house in order. To start widening your power base. To reduce the political pressure cooker that is building on the streets, before you are hit with an Iranian-style revolution. And just in case you are in any doubt, we are not going to stand by and let Islamic fundamentalism take over the region."

White House officials like to point out that not a single member of the Arab League is a true democracy.

Condoleezza Rice believes that the fall of Saddam Hussein will inspire a "march of democracy" across the Middle East.

So, people are right when they say there is an ulterior motive to an attack on Iraq. But it is not military occupation.

It is about denying radical Islamic groups access to weapons of mass destruction, oil reserves and control of the Middle East.

In the end, it does come down to oil. Naturally, Bush's friends in the oil business will benefit from a "Pax Americana" in Iraq.

But - so they believe - millions of ordinary Arabs will enjoy greater freedom and more access to power in their own countries.

Fanciful? Maybe. But this administration is determined to try.

It is prepared to withstand the temporary outrage of the international community along the way. And if necessary, it is prepared to do it alone.