A secret report from the US state department pours cold water on the "domino" theory of democratic change in the Arab world - the idea, promoted by Bush administration hawks, that removing Saddam Hussein from power in Iraq could set off a flourishing of democracy throughout the region.

Huge economic and social obstacles would make political change "difficult to achieve for a very long time", the report says, casting doubt on one of the key justifications President George Bush has cited for an attack on Iraq.

"Liberal democracy would be difficult to achieve," and even if electoral systems were introduced, anti-American feeling runs so strong that they could well elect radical Islamic governments hostile to Washington, according to the report, which was leaked to the Los Angeles Times.

The domino theory is central to the vision of several neoconservatives centred in and around the Pentagon, notably Paul Wolfowitz, the deputy defence secretary, and Richard Perle, the chairman of the defence policy board.

Iraqi democracy "would cast a very large shadow, starting with Syria and Iran but across the whole Arab world," Mr Wolfowitz told a Congressional committee recently.

Mr Bush emphatically endorsed the concept in a speech two weeks ago, predicting that "a new regime in Iraq would serve as a dramatic and inspiring example of freedom for other nations in the region".

Tony Blair, in contrast, has mentioned the need for Arab democracy in speeches promoting his stance on Iraq, but has not suggested he believes an invasion would automatically lead to democracies.

The state department report says that Middle Eastern societies are riven by problems, including "high levels of corruption, serious infrastructure degradation [and] overpopulation". This means that "political changes conducive to broader and enduring stability throughout the region will be difficult to achieve for a very long time," according to a department official who has seen the paper.

The state department refused to comment.

"I think Bush, Cheney and Rumsfeld do honestly believe [the domino theory]," said Thomas Carrothers of the Carnegie Endowment for International Peace, a dovish thinktank.

But "what's missing from it is the how, the actual process. The problem with most Arab leaders isn't that they don't understand democracy - it's that they have no intention of giving up power. There isn't an enlightenment effect to take place."

The state department, Mr Carrothers said, "have people closer to the actual politics of the region, and what they're hearing is: 'You guys invade Iraq, you can expect the fundamentalist groups will get a surge of support, we're going to have to crack down, and there will be a reduction in the political space.'"

Analysts close to the neoconservatives say they have no illusions about wholesale regime change through the region. Instead, they would expect neighbouring governments to feel pressurised into granting their populations more freedom.

"There is a broad understanding that we're not going to see the overthrow of existing governments, but rather a broad thrust for the liberalisation of these governments," said Patrick Clawson, deputy director of the more hawkish Washington Institute for Near East Policy, which is close to the state department.

"They'll resist bitterly, and there is a considerable risk of instability, but the process of democratic reform will be in the interests of regimes in the area.

"People say it's not clear if the Middle East can achieve Jeffersonian democracy - but I say Jeffersonian democracy included slaves, and it was another 140 years before women got the vote."

Nobody takes seriously, he said, "the idea that democracy's going to come to the Middle East like it came to Eastern Europe, in the space of a year or two".