NAJAF, Iraq -- Top Iraqi Shiite leader Ayatollah Mohammed Baqer al-Hakim returned to the Iraqi holy city of Najaf Monday, with his motorcade greeted by tens of thousands of people celebrating the end of his 23 years of exile in Iran.

"Yes, Yes, Hakim! Down, Down Saddam Hussein!" was chanted by the crowds, many of whom had been waiting for hours in the afternoon heat, AFP reported.

The 66-year-old Hakim, who heads the Supreme Assembly for Islamic Revolution in Iraq (SAIRI), crossed from Iran to Iraq on Saturday and has made a three-day tour through the mainly Shiite south of the country.

The crowds of men of all ages, many waving banners and portraits of Hakim, brought the pace of the cleric's long convoy to a crawl at some main insections as it rolled toward the center of Najaf and the shrine of the first Shiite Imam Ali (AS).

Sheep were also slaughtered at several points passed by the dozens of brand-new white four-wheel drives carrying the cleric, his aides and bodyguards. Pick-ups leading the convoy tossed out leaflets declaring that Hakim was returning to his birthplace to "rebuild an Islamic Iraq".

The SAIRI head was also greeted as he toured through Basra, the parched marsh lands, Nasiriyah and Samawa en route to Najaf.

Meanwhile, the new U.S. boss of postwar Iraq, Paul Bremer, flew in to Baghdad on Monday to take the helm of a troubled administration that has watched much of the nation descend into lawlessness and near chaos.

Bremer, a career diplomat tapped by U.S. President George W. Bush last week to replace retired U.S. General Jay Garner, arrived in the capital as the nation's new de facto ruler following a mass shakeup of the U.S. leadership in Iraq.

"The coalition did not come to colonize Iraq," said Bremer, 61, who will oversee the rebuilding of the country and its transition to a democratic government after the ouster of Saddam Hussein.

"We came to overthrow a despotic regime. That we have done. Now our job is to turn and help the Iraqi people regain control of their own destiny," he said upon arrival at Baghdad airport.

The U.S.-led administration here has faced blistering criticism over the slow pace of the rebuilding process and the virtual anarchy which has reigned since Saddam was toppled on April 9.

Many Iraqis still have no running water or electricity. Trash and sewage are rotting in the streets, and armed gangs are terrorizing the population. Hospitals have been stripped bare and the phones do not work. Garner, a folksy military man who did not establish an effective way to communicate with the Iraqi people, was placed under Bremer's

supervision, and press reports have said he will be out the door in one or two weeks. The general said the reports were "not true" while Bremer told reporters: "We intend to have a very effective, efficient and well-organized handover."

Speaking earlier as the two men first landed along with general Richard Myers, the chairman of the U.S. Joint Chiefs of Staff, in the southern city of Basra, Bremer glossed over any criticism of Garner's brief tenure on top.

"I also want to say how proud I am of the work my good friend Jay Garner and the people who are working for him, how proud I am of everything they have done here in the last couple of weeks under extraordinary circumstances," he said.

"I certainly intend to work with him in the next weeks here to get a bunch of serious milestones accomplished," he said.

In addition to the massive reconstruction of a nation battered by three wars in 23 years and more than a decade of crippling UN sanctions, Bremer will also guide Iraq's transition to an interim Iraqi government.

A U.S.-anointed council of former opposition leaders has been meeting with Garner and other U.S. officials ahead of a national congress expected by the end of May to select the government.

Many Iraqis have bristled at the notion that their postwar leadership would be hand-picked by the United States, and Bremer's diplomatic skills are expected to ease some of the concerns over the U.S. role here.

No date has been set for when the U.S.-led coalition would hand over power to Iraqis, or when an interim government would be able to prepare the way for elections.

"It's a wonderful challenge to help the Iraqi people basically reclaim their country from a despotic regime," Bremer said.

The reshuffle of the U.S. team is expected to lead to other departures in the coming weeks, according to an anonymous U.S. official quoted in Monday's New York Times.

Barbara Bodine, who had been Garner's administrator for the central Iraq region which includes Baghdad, left Sunday after less than three weeks in the country. U.S. officials said the move was routine.

But Bodine, who has been shifted to the State Department in Washington, told the Washington Post she had been informed of her recall in a late-night call in Baghdad on a phone that had only been installed hours before.