U.S. and British troops awaited the order to unleash a massive assault on Iraq on Wednesday after a U.S. deadline for President Saddam Hussein to give up power and seek exile expired.Saddam defied President Bush's ultimatum for him and his sons to leave the country by 8 p.m. EST, which is 4 a.m. local time on Thursday in Iraq. The world held its breath, awaiting the news that the war had begun.

U.S. and British troops moved into the demilitarized zone that straddles the Iraq-Kuwait border on Wednesday. The zone extends three miles into Kuwait and six miles into Iraq. Soldiers donned chemical suits at desert staging posts that were swept by fierce sandstorms.

Bush met with military planners, chaired a National Security Council meeting and was "allowing the time that he has given to pass," said spokesman Ari Fleischer.

As night fell on Washington, there was no sign from the White House on whether the fighting would start immediately after the deadline or be delayed for a little while.

On aircraft carriers and at land bases, pilots prepared for what is expected to be one of the most ferocious aerial bombardments in history.

Upward of 3,000 satellite-guided bombs and cruise missiles will be unleashed from sea and air on targets vital to Saddam's government to start the war, officials said.

The strategy, dubbed "shock and awe" by the U.S. military, is designed to destroy Saddam's air defenses and remove his command and control ability while stunning Iraqi troops to the extent that many will be too demoralized to resist.

British and U.S. aircraft dropped almost 2 million leaflets over southeastern Iraq urging Iraqi soldiers not to use weapons of mass destruction or torch oil wells, and advising them to lay down their weapons rather than die for a lost cause.

White House spokesman Ari Fleischer braced Americans for casualties. "It could be a matter of some duration. We do not know," he said.

U.S. planners' biggest fears are that the Iraqis may use chemical weapons or that Saddam loyalists hole up in Baghdad and force invaders to conquer the city street by street and house by house.

BASRA AN EARLY GOAL

U.S. defense officials and private analysts say one of the first objectives of an invasion would be to overwhelm regular army units and take Basra, about 40 miles from the Kuwait border and 340 miles southeast of Baghdad.

Simultaneously, other forces will enter the north in an effort to seize control of crucial oil fields before they can be set aflame.

Leaflets have told Iraqi forces to leave their tanks with their turrets reversed and to abandon vehicles in the open while returning to barracks if they wanted to live.

Aboard the aircraft carrier USS Abraham Lincoln, Vice Adm. Timothy Keating, commander of the U.S. Navy's 5th Fleet, prepared forces for the mission.

Iraq's information minister, Mohammed Saeed al-Sahaf, said in Baghdad the invaders were facing "definite death." Iraqi legislators vowed to die for their leader.

Bahrain offered Saddam sanctuary and a life with dignity to avert war but there was no expectation he would accept.
The U.N. aid official in charge of Iraq, Ramiro Lopez da Silva, said war would trigger a major humanitarian disaster in a country already crippled by more than a decade of sanctions

PHOTO CAPTION

A U.S. Airforce C-5 Galaxy prepares to take off at the joint U.S.-Spanish airbase of Moron, southern Spain March 19, 2003. (Marcelo Del Pozo/Reuters)