(Updates throughout)

By Khaled Farhan

KUFA, Iraq, May 25 (Reuters) - Powerful anti-American Shi'ite cleric Moqtada al-Sadr appeared in public for the first time in months on Friday, presenting himself as a champion of all Iraqis and demanding that U.S. troops get out of Iraq.

Sadr, who has not been seen since the start of a major U.S.-backed security crackdown in Iraq in February, also sought to stamp his authority on his feared Mehdi Army militia, calling on them to stop fighting Iraqi forces. Some U.S. officials and analysts say several factions have been disobeying his orders.

In a sermon at Friday prayers in the southern city of Kufa, the Shi'ite cleric, who draws his support mainly from poor Shi'ites, sought to portray himself as a national leader prepared to defend the interests of Sunnis and Christians too.

Dressed in traditional black robes and turban, he entered the mosque surrounded by guards and aides.

"I renew my demand for the occupiers to leave or to draw up a timetable for withdrawal, and I ask the government not to let the occupiers extend their occupation even for one day," he told thousands of worshippers.

The U.S. military says Sadr fled to Iran in January ahead of the launch of the Baghdad security plan, but aides to the young cleric insist he never left Iraq.

"Moqtada disappeared because there was some indication that he was wanted, but now it seems there are no signs that he is wanted. That is why he has come back," a senior member of the Shi'ite Alliance told Reuters.

While there will be much speculation as to why Sadr has chosen now to appear in public after staying out of sight for so many months, his sudden re-emergence comes at a time when Iraqi politics are in flux.

TIMETABLE

Sadr withdrew his six ministers from Prime Minister Nuri al-Maliki's government in April in protest at Maliki's refusal to set a timetable for a U.S. troop withdrawal, although he kept its 30 seats in the fractious ruling Shi'ite Alliance.

The main Sunni Arab bloc in the government is considering pulling out over what it says is growing sectarian violence and rampant corruption.

Maliki's weak and divided government is also under mounting pressure to curb violence, reach a political accommodation with minority Sunnis, and deliver basic services to Iraqis.

As part of his effort to refashion himself as a nationalist, Sadr said he was ready to cooperate with Sunni Arabs "on all issues", adding: "I am completely ready to defend them (Sunnis and Christians) and be their armour against their enemies."

The Mehdi Army is accused of fuelling Iraq's sectarian violence with hit-squad attacks on Sunnis. The Pentagon has called it one of the greatest threats to peace in Iraq.

The deputy U.S. commander in Iraq, Lieutenant-General Raymond Odierno, told the Washington Post he believed Sadr had returned to Iraq to reimpose his authority over the Mehdi Army, which he said appeared to be "cracking".

Sectarian murders in Baghdad appear to be on the rise again after three months of sharp declines. Police this week have reported finding about 30 bodies a day on average.

Such killings are typically blamed on Mehdi Army hit squads, although militiamen have largely kept off the streets since the start of the crackdown to avoid confrontations with U.S. troops.

(Additional reporting by Mariam Karouny in Baghdad)

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