US troops would face elite Iraqi soldiers defending Baghdad 'street by street'

American forces believe Saddam Hussein will order his most loyal soldiers to fight for Baghdad street by street against a ground invasion – creating an Iraqi version of the battle of Stalingrad.

Iraq was placed on a war footing yesterday when President Saddam divided his country into four military regions and put one son in control of the two cities where fighting is expected to be the most fierce if there is a US-led war. President Saddam said his son Qusay would personally direct the defence of Baghdad and the Iraqi leader's home town of Tikrit.

As well as retaining the position of supreme commander, President Saddam also holds the sole authority to order the use of surface-to-surface missiles and what is left of the Iraqi air force. There was no mention made yesterday of another of the President's sons, Uday, once regarded as the heir apparent. Qusay is now seen as the successor if the current regime were to survive.

America intends to launch a complex "rolling strike" against Iraq, utilising troops already in the region. Three powerful US armoured units – the First Cavalry Division, the First Armoured Division and the Third Armoured Cavalry Regiment – are still in America or Europe and will not be in the Gulf until mid to late April. They will probably be in a post-war stabilisation force.

The Pentagon, and independent military analysts, say the greatest challenge for US forces will be the fight for the Iraqi capital. British forces are expected to be used only in the country's south-east, near the city of Basra.

Baghdad presents a huge potential pitfall for an invading army. President Saddam is believed to have already decided to withdraw his best forces to the city.

In the 1991 Gulf War, he learnt that trying to fight in the desert left his troops vulnerable to American and British airpower. The Republican Guard and the elite Special Republican Guard are expected to form concentric circles around Baghdad, fighting street-by-street. In these circumstances, American high-tech weaponry would have less of an advantage.

In a reference to the Special Republican Guard, one senior US officer said: "The closer you get to Baghdad and the Special Republican Guard, the tougher the question of will. That's the million-dollar question – whether they'll have the will."

In some respects Baghdad is not suited for guerrilla-style fighting. The wide, Stalinist boulevards built by President Saddam for his own tanks could accommodate US and British Abrams and Challenger tanks.

But the older parts of the city, full of alleyways, could provide cover for fighters. "We have no intention of going door-to-door or house-to-house in a city of five million," said another US officer. "It's unbelievably complex, with underground tunnels and bunkers everywhere.If things go bad in a Mout [military operations in urban terrain] environment, they go bad quickly."

US forces might try to circle Baghdad and enforce a siege – perhaps waiting for an uprising inside the city. But America has also been involved in intensive planning, should it need to get involved in urban fighting.

Some of the $30m (about £20m) of supplementary special equipment purchased since last December by the US 101st Airborne Division included battering rams, grappling hooks, folding assault ladders and battle axes.

The shopping list also includedsniper rifles, Kevlar bullet-resistant helmets with built-in radio headsets and nearly 16,000 reusable plastic handcuffs.

Other elements of President Saddam's military preparations yesterday included the appointment of his cousin Ali Hassan al-Majid – who earned the nickname "Chemical Ali" for his part in the gassing of Kurds – as the military commander of Basra.