Billions of U.S. taxpayer dollars spent to train, equip and support Afghanistan security forces may end up wasted, according to the watchdog of reconstruction spending.

The special inspector general for Afghanistan reconstruction, retired Marine Gen. Arnold Fields, in what may be his final public event before he retires next month, painted a starkly pessimistic picture of what lies ahead in Afghanistan.

The build-up of the Afghanistan army and police is a key element in the Obama administration's plans to withdraw U.S. forces by the end of 2014. But Fields told the Commission on Wartime Contracting that the build-up is at risk.

"The United States lacks a comprehensive plan for building ANA (Afghan National Army) and ANP (Afghan National Police) facilities," Fields said. "The projects audited to date have been seriously behind schedule."

And Fields said it is not clear how Afghanistan will be able to sustain the big police and army building projects - such as barracks and training bases - once U.S. Forces withdraw.

"These issues place the entire U.S. investment of $11.4 billion in ANSF (Afghan National Security Forces) facilities construction at risk of not meeting Afghan needs or intended purposes and resulting in a large degree of waste," Fields said in his prepared statement to the commission.

Members of Congress repeatedly have criticized Fields for not being more aggressive in watching over the more than $56 billion in Afghanistan reconstruction. He has said it took time to establish his watchdog agency in 2008 and oversight in a war zone is difficult and dangerous.

Fields admitted that American taxpayers are "wary" of the U.S. investment in Afghanistan.

He said the U.S. plan calls for 884 projects for Afghanistan army and police to be completed by the end of fiscal year 2012. But Fields said only 133 are completed, 78 are under construction and 673 have not been started.