That’s the message that U.S. Defense Secretary Robert Gates got from President Hamid Karzai when he visited Afghanistan in December 2009. At that time, President Karzai told Sec. Gates that the Afghan government would not be able to shoulder the costs of the nation’s new security forces – both national police and military – before 2024.

Days later, in testimony before the Senate, General David Petraeus, commander of U.S. forces in the region, estimated that the cost of supporting Afghan security forces would total $10 billion annually.

With President Obama scheduled to make a major address on the timing of a drawdown of U.S. forces in Afghanistan tonight, these costs are one of several factors that indicate that even a significant withdrawal of combat troops will not provide much relief to U.S. taxpayers.

According to the Congressional Research Service (CRS) – the research branch of the Library of Congress – the Pentagon has spent $28.5 billion to train and equip Afghan security forces since Fiscal Year 2004, including $11.6 billion in the current fiscal year (FY2011) alone. The request for next year is even higher – $12.8 billion. Creating a viable national security force that can provide internal stability and conduct counter-insurgency operations is considered an essential condition for the eventual total withdrawal of U.S. forces. If Mr. Karzai is to be taken at his word, the United States will likely be called on to provide much of the support for Afghan security forces long after U.S. combat troops depart.

Likewise, the government has spent billions to support reconstruction, economic development and the creation of government institutions in Afghanistan through the Department of State and the U.S. Agency for International Development (USAID). According to CRS, these initiatives have cost over $25 billion to date, with a further $4.3 billion requested for the coming year. This work will become increasingly important to ensure broader support amongst Afghans for the new government.

An additional and unknown cost will be that of the increased number of civilian contractors that will likely be hired to perform some of the functions of the departing troops. According to CRS, there are already over 90,000 contractors (compared to the roughly 100,000 U.S. combat forces) in Afghanistan performing a broad range of combat support functions, including base and personal security. This number will almost certainly climb as U.S. forces – and those of other nations – depart.

Further, it is unclear how much savings a partial withdrawal of U.S. forces would generate. When President Obama announced his plans to “surge” an additional 30,000 troops to Afghanistan on December 1, 2009, he pegged the price of the additional forces at $30 billion, roughly $1 million per soldier ($33 billion was later appropriated by Congress). Yet a reduction of 30,000 troops is unlikely to yield corresponding savings. This is because past funding data shows that the costs of supporting forces in the field do not decrease proportionally to the reduction in troop levels, in part because the infrastructure that supports the remaining forces is still in place.

This is not to say that there are not sound policy reasons for a significant reduction, and the eventual total withdrawal, of U.S. forces from Afghanistan. But in the short term, at least, it is unlikely that a drawdown will do much to spare the U.S. taxpayer.

Newly confirmed Defense Secretary Leon Panetta has the unenviable task of picking up where retiring Secretary Gates left off. Mr. Panetta, please bring your checkbook.