WASHINGTON (Reuters) - The Iraq war may not dominate U.S. news reports as the carnage drops, but a new report underscores the financial burden of persistent combat that is helping run up the government's credit card.

"Funding for U.S. operations in Iraq and Afghanistan and other activities in the war on terrorism expanded significantly in 2007," the Congressional Budget Office said in a report released on Wednesday.

War funding, which averaged about $93 billion a year from 2003 through 2005, rose to $120 billion in 2006 and $171 billion in 2007 and President George W. Bush has asked for $193 billion in 2008, the nonpartisan office wrote.

"It keeps going up, up and away," Senate Budget Committee Chairman Kent Conrad said of the money spent in Iraq since U.S. troops invaded in 2003.

"We're seeing the war costs continue to spiral upward. It is the additional troops plus additional costs per troop plus the over-reliance on private contractors, which also explodes the costs," said Conrad, a North Dakota Democrat who opposed the war.

Since the September 11, 2001, attacks on the United States, Congress has written checks for $691 billion to pay for wars in Iraq and Afghanistan and such related activities as Iraq reconstruction, the CBO said.