America targeted 14,000 sites. So where are the weapons of mass destruction?

They were the reason the United States and Britain were in such a hurry to go to war, the threat the rank-and-file troops feared most.

And yet, after three weeks of war, after the capture of Baghdad and the collapse of the Iraqi government, Saddam Hussein's weapons of mass destruction – those weapons that President Bush, on the eve of hostilities, said were a direct threat to the people of the United States – have still to be identified.

Many influential people – disarmament experts, present and former United Nations arms inspectors, our own Robin Cook – have begun to wonder aloud if the weapons exist at all.

The public surrender of a senior Iraqi scientist could yet backfire against the US and Britain. Lieutenant-General Amer Hammoudi al-Saadi, who handed himself over to US forces yesterday, continued to proclaim that Iraq no longer holds any chemical or biological weapons. He should know: the British-educated chemical expert headed the Iraqi delegation at weapons talks with the United Nations.

The few "discoveries" trumpeted in the media – the odd barrel here, a few dozen shells there – have not been on a scale that could reasonably justify the unprovoked military invasion of a sovereign country, and in most cases have been proven to been no more than rumour, or propaganda, or a mixture of the two.

It could still be that, as American forces advance on Tikrit, Saddam's home town, chemical or biological weapons may be discovered, or even deployed by diehard Iraqi troops. But if the casus belli pleaded by George Bush and Tony Blair turns out to be entirely hollow – and it should be stressed that we can't yet know that – what does it say about their motivations for going to war in the first place? How much deception was involved in talking up the Iraqi threat, and how much self-deception?

As Susan Wright, a disarmament expert at the University of Michigan, said last week: "This could be the first war in history that was justified largely by an illusion." Even The Wall Street Journal, one of the administration's biggest cheerleaders, has warned of the "widespread scepticism" the White House can expect if it does not make significant, and undisputed, discoveries of forbidden weapons.

Before the war, American intelligence officials said that they had a list of 14,000 sites where, they suspected, chemical or biological agents had been harboured, as well as the delivery systems to deploy them. A substantial number of those sites have been inspected by the invading troops. Evidence to date of a "grave and gathering" threat: precisely zero.

Much of what has been unearthed points to something we knew about all along: the weapons programmes that Iraq ran before the 1991 Gulf War, before sanctions, before regular US and British bombing raids in the no-fly zones and before the UN weapons inspection regime that ran from 1991 to 1998.

US troops have discovered a few suspect barrels here, a sample bottle of nerve agent there, stacks of chemical suits and some drugs typically used to counteract the effects of a chemical attack, such as atropine and 2-pam chloride. According to many military experts, these finds suggest the vestiges of a weapons programme that has been dismantled, not one that is up and running. The US government argues that the weapons have been deliberately dispersed and hidden – a claim that would have more merit if there were any evidence of where the materials might have gone.

In his State of the Union address in early February, President Bush was quite specific about the materials he believed Saddam was hiding: 25,000 litres of anthrax, 38,000 litres of botulinum toxin and 500 tons of sarin, mustard and nerve gas. These days, he does not mention weapons of mass destruction at all, focusing instead on the liberation of the Iraqi people – as if liberation, not disarmament, had been the project all along.

The administration has shown its embarrassment in other ways. On day two of the war, Donald Rumsfeld, the Secretary of Defence, said finding and destroying weapons of mass destruction was the invading force's number two priority after toppling Saddam Hussein – itself a reversal of the argument presented at the UN Security Council.

A week later, Victoria Clarke, the Pentagon spokeswoman, pushed the issue further down the list, behind capturing and evicting "terrorists sheltered in Iraq" and collecting intelligence on "terrorist networks". Now we are told that hunting for weapons is something we can expect once the fighting is over, and that it might go on for months before yielding significant results. "It's hard work," a plaintive Ms Clarke said last week.

Nonsense, say the disarmament experts. "It's clear there wasn't much," said Professor Wright, "otherwise they would have run into something by now. After all, they've taken Baghdad." Hans Blix, the chief UN weapons inspector who spent four months badgering the United States and Britain in vain for reliable intelligence information about the whereabouts of lethal weapons, now says he believes the war was planned on entirely different criteria, well before his inspection teams went back into Iraq in December.

"I think the Americans started the war thinking there were some [weapons]. I think they now believe less in that possibility," he told the Spanish daily El Pais. "You ask yourself a lot of questions when you see the things they did to try to show that the Iraqis had nuclear weapons, like the fake contract with Niger."

Anxious to find a "smoking gun", a team of US disarmament experts has been set up to question Iraqis involved in weapons programmes, while others comb sites and analyse samples in the field using mobile labs.

The move has alarmed the weapons inspectors at the UN, where Kofi Annan, the UN secretary general, pointedly said last week: "I think they are the ones with the mandate to disarm Iraq, and when the situation permits they should go back to resume their work."

The US team has attempted to lure some of the inspectors, who are recognised as the sole legitimate international authority on Iraq's weapons programmes.

The latest theory being touted in Washington by the usual unnamed government sources is that the Iraqis have moved their weapons out of the country, very possibly into Syria. This claim appears to have originated with Israeli intelligence – which has every motivation for stirring up trouble for its hostile Arab neighbours – and has been bolstered by reports of fighting between Iraqi Special Republican Guard units and US special forces near the Syrian border.

Disarmament experts do not give the claim much credence. After all, any suspicious convoy or mobile laboratory would almost certainly be spotted by US planes or spy satellites and bombed long before it reached Syria.

But the notion does provide the hawks in Washington with a compelling plot device not unlike the McGuffin factor in Alfred Hitchcock's films – a catalyst that may or may not have significance in itself but that gets the suspense going and keeps the story rolling.

If the Bush administration should ever seek to turn its military wrath on Damascus, the weapons of mass destruction it is failing to find in Iraq might just provide the excuse once again.