"This report was put out by Democrats on Capitol Hill," White House press secretary Dana Perino was quoted by the Associated Press as saying. "This committee is known for being partisan and political."

"They did not consult or co-operate with the Republicans on the committee, and so I think it is an attempt to muddy the waters on what has been some positive developments being reported out of Iraq."

And some of the figures the report contains were labelled speculative by funding experts, the Washington Post newspaper reported.

'Lost earnings'

The report was written by Democratic members of Congress's Joint Economic Committee (JEC).

The BBC's Justin Webb in Washington says it was designed to shock Americans into stronger opposition to the war in Iraq.

The Democrats calculate that between 2002 and 2008 the campaigns in Iraq and Afghanistan will have cost the average US family of four about $20,900.

The report adds that the amount could rise to $46,400 over the next decade.

It cites costs such as interest payments on money borrowed from abroad to pay for the wars, lost investment in US businesses, and the cost of oil market disruptions.

Oil prices have surged since the start of the war in Iraq, from about $37 a barrel to more than $90 a barrel in recent weeks. The report says the rise has hit US consumers.

The chairman of the JEC, Democratic Senator Chuck Schumer, said the "backbreaking cost" of the war was becoming an unbearable burden for American families.

"What this report makes crystal clear is that the cost to our country in lives lost and dollars spent is tragically unacceptable."

He said: "The cost of the war... is becoming the first thing the people mention after the loss of life when they are opposed to this war and the people who mention it, many of them are not people who were against the war in the past."

The report estimates that both wars could cost a total of $3.5 trillion over the next decade.

The Democratic authors estimated that treating veterans could add more than $30bn to costs, including disability payments and lost earnings for veterans affected by post-traumatic stress disorder.