Pacifying the lawless capital is regarded as essential to establishing the authority of the incoming government and preparing for a significant withdrawal of American troops.

Strategic and tactical plans are being laid by US commanders in Iraq and at the US army base in Fort Leavenworth, Kansas, under Lieutenant- General David Petraeus. He is regarded as an innovative officer and was formerly responsible for training Iraqi troops.

The battle for Baghdad is expected to entail a “carrot-and-stick” approach, offering the beleaguered population protection from sectarian violence in exchange for rooting out insurgent groups and Al-Qaeda.

Sources close to the Pentagon said Iraqi forces would take the lead, supported by American air power, special operations, intelligence, embedded officers and back-up troops.

Helicopters suitable for urban warfare, such as the manoeuvrable AH-6 “Little Birds” used by the marines and special forces and armed with rocket launchers and machineguns, are likely to complement the ground attack.

The sources said American and Iraqi troops would move from neighbourhood to neighbourhood, leaving behind Sweat teams — an acronym for “sewage, water, electricity and trash” — to improve living conditions by upgrading clinics, schools, rubbish collection, water and electricity supplies.

Sunni insurgent strongholds are almost certain to be the first targets, although the Shi’ite militias such as the Mahdi army of Moqtada al-Sadr, the radical cleric, and the Iranian-backed Badr Brigade would need to be contained.

President George W Bush and Donald Rumsfeld, the defence secretary, are under intense pressure to prove to the American public that Iraq is not slipping into anarchy and civil war. An effective military campaign could provide the White House with a bounce in the polls before the mid-term congressional elections in November. With Bush’s approval ratings below 40%, the vote is shaping up to be a Republican rout.

The Iraqi government, when it is finally formed, will also need to demonstrate that it is in charge of its own seat of government. “It will be the second liberation of Baghdad,” said Daniel Gouré, a Pentagon adviser and vice-president of the Lexington Institute, a military think tank. “The new government will be able to claim it is taking back the streets.”

Larry Wilkerson, former chief of staff to Colin Powell at the State Department, said a crackdown in Baghdad was one of the few ways in which a fresh Iraqi government could bind the new national army and prove its mettle.

“They have to show they can liberate their own capital,” he said. “Baghdad is the key to stability in Iraq. It’s a chance for the new government to stand up and say, ‘Here we are’. They can’t do that if they are hunkered down in bunkers.”

The operation is likely to take place towards the end of the summer, giving the newly appointed government time to establish itself. If all goes to plan, US troop withdrawals could take place before the end of the year. In the absence of progress by then, the war may come to be seen by the American public as a lost cause.

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