BAGHDAD (MCT) — In the coming days, the hard-line Shiite cleric Muqtada al-Sadr has a crucial decision to make: whether to renew the six-month freeze on activities of his Mahdi Army militia that has been credited with helping bring down the levels of violence in Iraq.

A refusal to extend the cease-fire could have a profound impact on the successes scored so far by President Bush's military surge strategy, raising the specter of a return to the sectarian Sunni-Shiite killings that pushed Iraq to the brink of civil war as well as a possible increase in the number of attacks against U.S. forces.

As the deadline for the expiration of the declared cease-fire approaches, U.S. officials say they have noted an increase in the number of attacks by Shiite extremist groups believed to be backed by Iran, suggesting support for the cease-fire is starting to wane among Sadrist supporters.

U.S. officials have repeatedly said they expect the cease-fire to be renewed, but aides to al-Sadr in the holy Shiite city of Najaf hinted Wednesday that an extension is far from certain.

The aides said that they have given al-Sadr a series of reports on the cease-fire's impact on the al-Sadr movement in various Iraqi provinces and that he would decide by Saturday whether or not to renew it.

If al-Sadr does not announce an extension by Saturday, "it means the freeze has finished," said his spokesman, Sheikh Salah al-Obeidi.

Addressing reporters in Baghdad, U.S. military spokesman Rear Adm. Gregory Smith praised the role of the Mahdi Army's suspension of hostilities in bringing down the violence.

"We hope and expect it will continue," he said of the cease-fire. "Their steps have been very positive in reducing violence, and we expect that to be the same in the future."

U.S. commanders say they noticed a sharp fall in the number of attacks against U.S. forces by Shiite militias immediately after the cease-fire declaration in August, as well as a steep reduction in the number of sectarian killings of Sunnis in and around Baghdad.

That helped encourage Sunnis to turn against the extremist al-Qaida in Iraq organization, which had been fueling Sunni violence against Shiites, leading to a 75 percent reduction in the number of Iraqi civilian casualties between February 2007 and January this year, according to Smith. The number of U.S. casualties fell from a peak last year of 126 in May.

For al-Sadr, who rose to prominence as one of the most powerful figures in Iraq for his tough stance against the U.S. occupation, the decision to renew presents something of a dilemma, however.

Al-Sadr declared the freeze after fighting erupted in the holy city of Karbala between his militia and local police loyal largely to a rival Shiite organization, the Badr Organization. The Mahdi Army was widely blamed for the violence, and the cease-fire helped restore al-Sadr's standing among ordinary Shiites alienated by the Mahdi Army's growing reputation for thuggery.

U.S. and Iraqi officials say al-Sadr has used the cease-fire to streamline and reorganize his militia, weeding out criminals and those disloyal to his leadership.

But at the same time, al-Sadr has risked alienating a core constituency which views the Mahdi Army as an army of resistance against the U.S. The recent rise in attacks by Shiite extremists, known as Special Groups, suggests he may be losing control over his key commanders to hard-liners whom the U.S. military believes receive training and funding from Iran.

A series of raids and arrests by the U.S. and Iraqi armies against Mahdi Army commanders, notably in the southern Iraqi cities of Diwaniyah (in Qadisiyah province) and Amara (in Maysan province), have further fueled dissatisfaction with the cease-fire among Sadrists, who say the U.S. and the Iraqi government have taken advantage of the cease-fire to weaken the Mahdi Army.

Sadrist lawmaker Bahaa al-Aaraji said the Sadrist movement wants guarantees from the government that Mahdi Army members will not be targeted by U.S. and Iraqi forces if the cease-fire is to be extended.

"We want these promises, and if the government gives promises, the freeze will continue," he said. "The ball now is in the government's court."

In a report earlier this month, the Brussels-based International Crisis Group recommended that the U.S. military and the Iraqi government make a greater effort to accommodate the Sadrists, warning that the Mahdi Army remains a powerful force that could easily disrupt the successes of the surge and complicate plans to draw down U.S. troops.

"Among Sadrist rank-and-file, impatience with the cease-fire is high and growing. They equate it with a loss of power and resources and eagerly await Muqtada's permission to resume the fight, as early as this month," the report said.