U.S. Army soldiers stroll past two bronze busts of former Iraqi president Saddam Hussein in the Green Zone in Baghdad in March 2009 on the sixth anniversary of the U.S.-led invasion of Iraq. The war began with a missile and bombing attack on south Baghdad before dawn on March 20, 2003.

Umm Qasr, Iraq ? The drop in oil prices has forced Iraq’s military and police to put recruiting on hold even as the U.S. hands over more responsibility for protecting the country.

The freeze is stalling efforts to hire Sunni ex-insurgents and has prompted the Iraqi military to transfer hundreds of soldiers to the navy to protect vital oil installations in the Persian Gulf.

Iraq will also have to scale back purchases of equipment and weapons, raising new questions about its ability to defend the country’s borders and prevent a resurgence of violence.

All this comes as the Iraqi military is preparing for the 2011 departure of U.S. forces, who often provide everything from clean drinking water to fuel.

It’s unlikely to affect the withdrawal schedule, which was set in a security agreement that took effect Jan. 1. But unless oil prices rebound, the crisis could threaten hard-won security gains.

The freeze began without fanfare in the police ministry in December and expanded when the government had to revise its 2009 budget early this year.

This month, Iraq’s parliament passed a $58.6 billion budget, which was sharply reduced twice from $79 billion after oil prices plummeted from a high of nearly $150 a barrel last July to $51 a barrel on Friday. Iraq relies on oil sales for about 90 percent of its revenue.

One of the biggest concerns is the government effort to bring tens of thousands of Sunni fighters who turned against al-Qaida in Iraq into the security forces to keep them employed and away from violence.

The government promised to hire 20 percent of the so-called Sons of Iraq into the army or police, but the transition has gone slowly.

The transfer of more than 91,000 Sunnis who left the insurgency and joined security groups initially funded by the U.S. to Iraqi government control is due to be completed next month. Just over 3,000 have joined the army and police, although Iraq’s government is paying the others a small salary.

Brig. Gen. Frederick Rudesheim, a deputy commander of U.S. forces in Baghdad, said the hiring freeze has slowed the process even further.

“There has been a commitment, a previous commitment to reintegrate the Sons of Iraq into security forces, primarily the police and perhaps the army in fairly large numbers,” he told reporters recently. “That has happened but not to the degree that was anticipated.”