WASHINGTON, Dec 21: The cost of America’s war against terror, by the end of this year, would exceed what Washington spent during the Vietnam war, says the Congressional Research Service, which prepares policy guidelines for US lawmakers.

Since the attacks of Sept 11, 2001, the US Congress has approved more than $500 billion for the wars in Iraq and Afghanistan and for terrorism-related operations elsewhere.

The Bush administration is already drafting a supplemental request for more than $100 billion in additional funds to meet the ever-increasing cost of the two wars.

This is on top of the $70bn already approved for this fiscal year. When this addition $100bn is added, the expenses would be over 50 per cent more than originally projected for fiscal 2007, making it by far the costliest year since the 2003 invasion.

This would also bring overall expenditures to $600bn, exceeding those for the Vietnam war, which, adjusted for inflation, cost $549bn, says the CRS report.

The Vietnam war cost an inflation-adjusted $121bn at its height in 1968 while the US is expected to spend more than $170bn in Iraq by the end of this year.

The war against terror has continued for a little more than five years while the United States started sending military advisers to Vietnam as early as 1950. In 1956, these advisers assumed full responsibility for training the Army of the Republic of Vietnam. Large numbers of American combat troops began to arrive in 1965 and the last left the country in 1973.

At his news conference on Wednesday, President Bush also announced plans to expand the US military, which would further accelerate the already-rising costs of war.

Some media reports have warned that even this additional $100bn may not be enough to fund a planned deployment of 30,000 to 40,000 US troops in Iraq.

According to the non-partisan Congressional Research Service, the Iraq war alone has so far cost more than $350bn.

Media reports noted that the cost of the war in Iraq has risen dramatically as the security situation has deteriorated and more equipment is destroyed or worn out in harsh conditions. The US Army, which has borne the brunt of the fighting, would receive about half of the request, a reflection of the wear and tear that the war has had on soldiers and their equipment.

An additional $9.8bn is being sought for training and equipping Iraq's and Afghanistan's security forces.