AIKEN - White House hopeful Barack Obama on Saturday criticized the use of private security contractors in a costly war in Iraq and said they are raising the risk for U.S. troops because Iraqis don't distinguish between the forces. He also criticized the pay disparity between soldiers and private contractors.

"You've got young men and women signing up to serve, willing to spill blood for America. How could they be treated less well than private contractors?" Mr. Obama told a crowd of more than 1,400 gathered in and around South Aiken High School's gymnasium in this early voting state. "And these private contractors, they go out and they're spraying bullets and hitting civilians and that make it more dangerous for our troops."

Blackwater USA, the private contractor that provides heavily armed security for U.S. diplomats serving in Baghdad, has been under intense scrutiny in recent weeks. Security forces employed by the company are accused of killing 13 Iraqi civilians in central Baghdad last month.

North Carolina-based Blackwater - which Mr. Obama did not mention by name - contends its employees came under fire first, but the Iraqi government and witnesses have disputed that, saying the guards opened fire without provocation.

Mr. Obama has turned his campaign's focus this week on the Iraq war, noting his strident opposition to the war and his opponents' acquiescence to a conflict that he says makes it more difficult to take care of health care and other pressing domestic needs.

Earlier Saturday in Ottawa, Ill., Mr. Obama told a crowd of about 600 that when "this war is over, we can finally get back to facing the challenges we face here at home, the challenges you're grappling with every day."

The first-term Illinois senator said the war now costs between $10 billion and $12 billion a month. He noted that President Bush had vetoed a $35 billion measure expanding a children's health program and wants almost $190 billion for military operations in Iraq and Afghanistan.

Mr. Obama reminded the crowd of United Auto Workers members in Illinois and the crowd in Aiken that he opposed invading Iraq at a time when most other politicians - including chief rivals Hillary Rodham Clinton and John Edwards - supported it. Mr. Obama expressed his opposition in the fall of 2002 when he was a state senator and considering a run for the U.S. Senate.

He said he would pull a division or two of U.S. troops out of Iraq every month and leave only enough there to protect the embassy and diplomats.