Even before a US deadline was up for the Iraqi leader to leave, US and British warplanes ranged across southern and western Iraq, bombing long-range artillery, a surface-to surface missile system and elements of the Iraqi air defenses that pose a threat to US forces, US defense officials said.

Coalition aircraft also showered Iraqi troops with "capitulation leaflets" giving detailed instructions on what to do to avoid attack, the US Central Command said. "I do not think our potential adversary has any idea what's coming," said Air Force Colonel Gary Crowder, chief strategist at the Air Combat Command.

Thousands of precision bombs and missiles will be used in the first day of a US air campaign, 10 times the number dropped in the opening the 1991 Gulf War, he said.

"The effect that we are trying to create is to make it so apparent and so overwhelming at the very outset of potential military operations that the adversary quickly realizes that there is no real alternative here than to fight and die or to give up," he said.

The air strikes would open 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.

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.

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

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 others move north up the Euphrates River valley toward Baghdad.

The Iraqi capital, shuttered and quiet late Wednesday as the 48-hour US ultimatum for Saddam Hussein and his two sons to leave the country ran into its final hours, was expected to be the 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.

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.

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 18 Iraqi soldiers crossed into Kuwait and surrendered to US troops, a US military source said.

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.

WAR.WIRE