The US and Britain have taken a big gamble by justifying Israel's third invasion of Lebanon because an Israeli failure to achieve its objectives will undermine their own position in the Middle East.

Vulnerable in Iraq and unpopular across the region, the English-speaking allies run the risk of losing even more friends and influence without much progress against Arab and Muslim groups and governments which oppose their plans for the region.

US Secretary of State Condoleezza Rice has described the violence in Lebanon as the birth pangs of a new Middle East and analysts say the Bush administration saw the conflict between Israel and the Lebanese group Hizbollah as a chance to disarm Hizbollah and punish their allies Syria and Iran.

In the process, the Israeli offensive would intimidate the Palestinian group Hamas, which refuses to recognise the Jewish state or abandon armed struggle to regain lost land.

But Israel has already had to adjust its strategy, playing down expectations that Hizbollah will unilaterally release the two Israeli soldiers it captured on July 12 or that the Lebanese government will take the initiative in disarming Hizbollah.

Israeli officials now say the immediate goal is to inflict as much damage as possible on Hizbollah before a ceasefire and that destroying all its rockets will not be possible. It is doubtful Israel can push Hizbollah so far from the border that its missiles can no longer reach Israel.

Mainstream commentators even in the US and Israel have started to question the likelihood of success in the Lebanese campaign, drawing parallels with the US and British failure to turn Iraq by military might into a peaceful bastion of democracy and pro-Western sentiment.

Bret Stephens, editorialist at the conservative Wall Street Journal, said: "If it (the war) continues as it is, Israel is headed for the greatest military humiliation in its history."

Aluf Benn, analyst in the Israeli newspaper Haaretz, said Prime Minister Ehud Olmert was making a final attempt to show the war as a victory rather than a draw, and the objective now was to see European troops deploy in a buffer zone along the border.

But for Hizbollah, any outcome that allows the organisation to survive and leaves large sections of the population sympathetic is a victory.

Olmert said yesterday that his army had entirely destroyed the infrastructure of Hizbollah and disarmed the movement "to a large degree".

But Hizbollah is also a political and religious movement with deep roots among Lebanese Shi'ites, the largest political force in the country's largest community. It continues to fight and it can easily replace its arsenal.

The US, Israel and Britain are pinning their hopes on an international force to deploy along the border and help the Lebanese army disarm the guerillas. But the record for such forces in Lebanon is not one of any success.

The danger for Washington and London is that a compromise outcome in Lebanon, after so much death and destruction, will further undermine their credibility in the Middle East and cast more doubt on the judgment of their leaders.

They have already embarrassed the few Arab friends they have left - such as Egypt, Jordan and Saudi Arabia, who face popular outrage that their appeals for a ceasefire have fallen on deaf ears.

Their campaign for democracy in the Arab world, in which they invested so much political capital over two years, has run out of steam and into deep contradictions.

The US has no high-level contacts with the major players - Iran, Syria, Hamas, Hizbollah and the Iraqi insurgents.

Even Lebanese Prime Minister Fouad Siniora, one of the most pro-American politicians in the region, told Rice last week that she need not come to Beirut unless she can bring a ceasefire.

If worst came to the worst, Hizbollah's sympathisers among the Iraqi Shi'ites could turn on US and British troops, possibly turning failure there into disaster.

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