US ground forces in central Iraq are gathering fresh combat power, probing enemy defences and allowing time for allied air power to weaken Iraq's Republican Guard around Baghdad before launching a multi-pronged attack.

US ground forces in central Iraq are gathering fresh combat power, probing enemy defences and allowing time for allied air power to weaken Iraq's Republican Guard around Baghdad before launching a multi-pronged attack.

The speed of the initial allied ground attack into Iraq from Kuwait last week led many to assume Baghdad would be assaulted soon, but now that appears to be many days away.

Severe sandstorms, for one thing, are affecting the timetable. Apache helicopters that made an initial round of strikes against armour of the Medina division of the Republican Guard on Monday have been grounded since. More Apaches are being brought to the area.

A key question was whether the Republican Guard troops - the best trained and equipped of Saddam Hussein's military forces - would make the first move by coming out of their dug-in positions on the outskirts of Baghdad, either to attack or to pull back into the urban centre.

Some reports from the battlefield today indicated a portion of the Al Nida armoured division of the Republican Guard was driving south toward US forces. Others said hundreds of suspected paramilitary forces in civilian vehicles were on the move in roughly the same direction.

Major General Stanley McChrystal, vice director of operations on the Pentagon's Joint Staff, said he had seen reports of Republican Guard units moving south but the situation was unclear.

If there is to be a battle for Baghdad - and US war planners hope they can topple Saddam's government without one - it appears the spearheading units, the 1st Marine Division and the Army's 3rd Infantry Division and 101st Airborne Division, are in no hurry to begin.

First they want US and British air power to pound the Republican Guard troops protecting the capital. During the 1991 Gulf War, the Republican Guard was hit with air strikes until US officials believed its firepower has been reduced by 50% before the main ground war began.

Iraq's regular army units have not put up much of a fight, although irregular forces like the Fedayeen Saddam - shock troops not under the military's command - have launched guerrilla-style raids.

Major General Victor Renuart, director of operations for Central Command, which is running the war, told reporters that an important aspect of the original war plan was to close quickly on the Republican Guard divisions "because they are so key to Saddam's success."

But as for when US forces would open a full-scale attack, Renuart said that would be a judgment call for General Tommy Franks, the top commander, in close consultation with his battlefield leaders.

The 3rd Infantry, with more than 200 tanks and other armoured vehicles, has been approaching Baghdad from the south, on the west side of the Euphrates River. The 1st Marine Division is driving on a parallel route on the east side of the Euphrates, and at some point the 101st Airborne division may leapfrog to the west or north of the capital, defence officials said.

The 101st Airborne - the air assault unit known as the Screaming Eagles - has moved its 3rd Brigade within striking of Baghdad, according to Colonel Michael Linnington, the brigade commander.

"We are one tank of fuel from Baghdad,' he told an Associated Press reporter travelling with him today. His and other airborne units were paralysed by persistent storms.

"The 101st is grounded and we're not doing what we do best, which is air assault operations and attacks,' he said. "Once we get the weather break we will restore the offensive to the north.'

He said the division's 1st Brigade was expected to join his unit by Thursday and the 2nd Brigade soon afterward. That would bring the division up to its full strength of 20,000 troops.

"When the Screaming Eagles strike, everybody will know,' he said.