The U.S. military has begun sending thousands of battered Humvees and other war-torn equipment home as more Iraqi units join the fight against insurgents and American units scheduled for Iraq duty have their orders canceled.

In the last four months, the Army has tagged 7,000 Humvees and 17,000 other pieces of equipment to be shipped to the United States to be rebuilt. They then will be distributed among active and reserve units at home, or possibly returned to equip Iraqi security forces.

The military said the shipments will result in a reduction in the amount of U.S. equipment in Iraq, a cut made possible because the area patrolled by American troops is shrinking. The move also anticipates that the number of American troops in Iraq will decline.

Countrywatch:Iraq

"This is all a byproduct of Iraqi forces accepting battle space and U.S. forces being displaced, which has allowed our government to decide not to send more forces," said Col. Jack O'Connor, commander of the U.S. Army Materiel Command's sustainment brigade in Iraq.

In one such move Monday, the U.S. Army's 1st Brigade Combat Team, 4th Infantry Division, based in Fort Hood, Texas, transferred responsibility for more than 235 square miles just north of Baghdad to the Iraqi Army's 9th Division.

Pentagon officials have said that the 132,000 U.S. troops in Iraq could be reduced to about 100,000 by the end of the year, if security doesn't further deteriorate.

Four combat brigades, in Texas, Alaska and Colorado, were notified this week that they will deploy to Iraq late this year. The roughly 21,000 soldiers would replace troops heading home from Iraq, and do not signal a change.

But analysts say that removing so much equipment now suggests commanders are laying the groundwork for an extensive reduction.

"It is much harder to move equipment than it is to move people," said Loren Thompson of the Lexington Institute. "So if the Army is increasing its movement of equipment out of the country, that may signal that it expects fewer soldiers in Iraq six or 12 months from now."

U.S. military commanders in Iraq have refused to set a timetable for a complete withdrawal of coalition troops, saying such a drawdown would be based on ground conditions.

O'Connor said the exodus of American rubber and steel from Iraq is scheduled to continue into the fall. Equipment headed back to the United States includes armored vehicles used by soldiers on patrols as well as many unarmored vehicles typically used inside the boundaries of secure U.S. military posts.

In most cases, a unit returning home from Iraq has left its equipment behind for the unit sent to replace them. But as more units rotate home between June and September, fewer U.S. units will be sent in behind them, O'Connor said.

At least two brigade-size units, totaling about 6,500 soldiers, that were scheduled to deploy to Iraq have been told to stay home, he said.

Often, the military is able to fix equipment in Iraq or in nearby countries.

Deep inside a depot at Camp Anaconda, about 50 miles north of Baghdad, broken trucks and eight-wheeled Stryker troop carriers are lined up for service by Army mechanics. In the case of the Strykers, manufacturer General Dynamics has set a major repair depot in the Middle East.

Most of what's being returned to the United States are vehicles and aircraft that need total rebuilds from the damage of years of operating the hot and dusty Iraqi environment, O'Connor said. From Humvees, manufactured by AM General, to helicopters to tanks, the equipment will enter a multi-billion-dollar repair program — known as reset — that rebuilds equipment for future wars.

The brigade from Materiel Command oversees and anticipates equipment needs of incoming and outgoing military units, O'Connor said. As more units stay home and Iraqis take control of larger areas, O'Connor said there will be a push in the months ahead to "clean up the battlefield" by removing equipment that is no longer needed.

Under a plan announced by Iraqi Prime Minister Nouri al-Maliki, Iraqi security forces will take responsibility for security in all of the country's 18 provinces within 18 months.

"With the talk of getting home by '08, we're leaning forward and trying to get all of that stuff out," O'Connor said. "We've got to rebuild an Army that's at war, and then make it ready for the next war. Clearly there are some challenges."

Getting equipment home after more than three years in Iraq is among the military's most cumbersome tasks ahead, O'Connor said.

Following the Gulf War in 1991, for example, it took two years for the military to recover its equipment — after a six-month deployment and a ground campaign lasting roughly 100 hours.

And the cost of repairing the equipment once it's back is huge. The backlog already is measured in years and some analysts say the price tag could exceed $50 billion.

U.S. officials at the Materiel Command in Virginia also have said they are in the midst of discussions on whether to equip Iraq's Army with equipment left behind by U.S. units.

Pulling equipment from Iraq also suggests that the U.S. military is looking past Iraq, rebuilding itself for some future conflict. But Steve Kosiak, analyst with the Center for Strategic and Budgetary Assessments, said that rebuilding the military while it is still at war may be not be easy.

It could be years after soldiers leave Iraq before the military is fully prepared, he said.

"There's going to be a window where the capability of the U.S. military is not what we'd want it to be," Kosiak said. "They're not going to be as prepared to go into another conflict."