Facing a far more ambitious task than in 1991, when it drove Iraqi invaders from Kuwait, the US military must quickly to seize control of a country the size of California, capture heavily defended Baghdad and keep casualties and war damage to a minimum.

Deafening air strikes have been designed to paralyze the Iraqi regime and military, opening the way for near simultaneous land offensives and airborne assaults as US and British forces pounce on military objectives checkerboard style, according to Pentagon officials and analysts.

"The United States is going to clearly prevail, and in fairly short order, against any Iraqi military," a senior US defense official told AFP.

"I guess there is always concern about casualties, there is certainly concern about what Saddam Hussein might do with respect to use of weapons of mass destruction, whether its chemical or biological," he said.

"But what I expect is the world will see a very professional, aggressive military action," he said.

Thousands of precision guided weapons, the latest high-tech reconnaissance and communications, new and still secret electronic warfare weapons will be overlaid on the brute force provided by tens of thousands of soldiers lunging out of the Kuwait desert in tanks, armored vehicles and assault helicopters.

At least part of the force is expected to sweep eastward to cut off the southern port of Basra while armored forces race north up the Euphrates River valley toward Baghdad.

The Iraqi capital, shuttered and quiet as a 48-hour US ultimatum for Saddam Hussein and his two sons to leave the country ran down to its final hours Wednesday night, was expected to be a focus of an intense US air campaign designed to isolate the Iraqi leadership by hammering its security forces and severing communications.

"Baghdad is not a safe place now or in the immediate future, for all the obvious reasons," said the US defense official.

The first 48 hours of an air war could see some 3,000 precision bombs raining down on leadership command posts, Republican Guards, communications networks and air defenses in hopes the regime will crumple from "shock and awe."

"What we're going to see is a very, very intense...use of precision weapons that will compress the impact on the Iraqis probably by a factor of ten over what happened before -- and properly applied that means that you will impose a strategic paralysis on Iraq," retired Colonel John Warden, the strategist who mapped the air campaign in the Gulf War, said in a television interview.

A key test of strength for the Iraqi regime will be on the road south of Baghdad where half of its six Republican Guard divisions are located.

"We're prepared for a situation where the Iraqi military offers stiff resistance and is organized in its execution of military operations," Vice Admiral Lowell E. "Jake" Jacoby, director of the Defense Intelligence Agency (DIA) told the Washington Post. "There is a very real likelihood, though, that resistance could collapse very quickly."

Pentagon officials said Republican Guard units have taken up defensive position, apparently to ride out the coming storm.

"They are dispersed out of garrison. It looks like they just want to survive," said a defense official.

Regular Iraqi military units, manned by conscripts with little reason to be loyal to the regime, were expected to fold quickly in the face of a US advance.

Defections already have begun on the frontlines, where 15 Iraqi soldiers crossed into Kuwait and surrendered to US troops, according to a US military officer.

The US military blanketed southeastern Iraq with nearly two million leaflets Wednesday, warning the Iraqi military not to use chemical weapons or set fire to oil fields and assuring civilians that coalition force meant no harm.

Radio broadcasts also were beaming in messages aimed at undermining the Iraqis will to resist.

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