WASHINGTON -- Mounting a war in Iraq may cost an extra $24 billion by the end of the first month's fighting, the U.S. Congressional Budget Office forecast Friday. Key estimates were:

-- Sending in the heavy ground force already amassed in the Persian Gulf region would have cost about $14 billion on top of the usual operating costs of the military.

-- The first month of combat would cost $10 billion, declining to eight billion dollars a month.

-- Returning forces to home bases would cost nine billion dollars.

-- Occupation after fighting ends could cost one billion to four billion dollars a month.

-- There is no way to estimate the cost of foreign aid.

Regardless of the composition of the force used, there were many unknowns about a war, the Congressional Budget Office (CBO) said in its interim analysis of President George W. Bush's budget plans.

"If the Iraqi leadership or selected elements of its military capitulated quickly, ground combat could be short, as in operation Desert Storm," the bipartisan office said.

"If urban fighting was protracted or Iraq used chemical or biological weapons against regional military or transportation facilities, the war could last longer," it warned. "Given such uncertainty, CBO's estimates of the monthly costs of operations exclude expenditures for decontaminating areas or equipment affected by chemical or biological weapons."

A war with Iraq could lead to substantial costs in later years, it said, but the CBO did not include such costs because they could not be assessed even roughly or they depended on uncertain policy decisions.

The United States might provide Iraq with funds for humanitarian assistance and reconstruction, and it might provide substantial aid to allies and other friendly nations in the region.

"Attaching estimates to any such costs would be quite speculative," the office said.

The CBO estimate is highly regarded because its members include both Republicans and Democrats.

The $1.9 trillion bill would include $140 billion for military costs, $500 billion for peacekeeping, $105 billion for reconstruction, $78 billion in the impact from higher oil markets and $391 billion for the wider economic impact. A long war and occupation lasting five years, with five years of rebuilding, would cost $1.47 trillion dollars for the US. economy, their study said. (AFP)