WASHINGTON - The United States risks squandering more than $11 billion if it does not come up with adequate plans for building and maintaining facilities for Afghanistan's growing security forces, a US watchdog said.

A new audit released on Wednesday by the special inspector general for Afghanistan reconstruction, or SIGAR, said US officials working to build up local police and soldiers, a key task in ensuring Afghanistan does not succumb to the Taliban when foreign forces withdraw, had failed to provide long-term construction plans for some 900 local security facilities.

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The watchdog began its probe when other investigations revealed that the US component of the NATO training mission in Afghanistan was unable to produce planning documents "describing the size, location or use of Afghan National Security Force facilities, such as Afghan National Army garrisons."

The audit said the absence of comprehensive, long-term plans could result in serious waste since the United States is expected to pour funds into training and equipping Afghan forces for years.

Auditors recommended that US commanders develop long-term maintenance and building plans and an updated framework that could reflect what may be a larger force of Afghan soldiers and police than originally expected, possibly 400,000 strong.

Impoverished Afghanistan isn't expected to be able to pay for more than a fraction of the cost of its own security forces for years. According to the World Bank, Afghanistan's GDP was at last count about $12 billion, far less than the $113 billion the United States is spending there annually.

A bewildering maze of aid and training programs in Afghanistan has had only mixed results since the ouster of the Taliban regime in 2001.

The United States has spent over $29 billion toward training and equipping Afghan security forces, including $9 billion set aside for fiscal year 2010.

While Afghan forces now number around 266,000, serious doubts remain about whether they will be ready to take over for foreign troops by the end of 2014 as hoped.

The Obama administration is seeking to show progress in Afghanistan so it can begin pulling out its force of almost 100,000 in July.