U.S. reconstruction projects worth billions of dollars will be nearly impossible to monitor following the 2014 troop drawdown in Afghanistan, when U.S. oversight workers won't be able to go into most of the country.

Access to projects has already shrunk dramatically as U.S. bases close and troops leave, taking security and medical support with them.

Only about 45 percent of the country is currently safe for U.S. civilian oversight personnel, according to a letter from the top U.S. watchdog in Afghanistan to the State Department, U.S. Agency for International Development and Department of Defense.

"It is clear that everyone working in Afghanistan, including SIGAR, will struggle to continue providing the direct U.S. civilian oversight that is needed in Afghanistan," wrote Special Inspector General for Afghan Reconstruction John F. Sopko.

So far in 2013, Sopko said SIGAR staff members were unable to visit the sites of projects worth $72 million because of security issues. Oversight personnel and contracting officers have also been unable to monitor their projects outside the limited safe areas.

SIGAR identified "oversight bubbles" where U.S. presence will allow agencies to visit project sites, but outside those bubbles, agencies will have to get creative to keep contractors accountable.

Inadequate oversight wastes money on projects that fall behind schedule, rack up excessive costs from unmonitored contractors, or are so poorly built they're nearly unusable.

By the end of 2014, the safe areas will include parts of Kabul, Kandahar, Balkh and Herat and Helmand provinces, or only about 20 percent of the country, according to a map obtained by The Washington Examiner. And that's the best-case scenario, according to SIGAR.

"We have also been told by State Department officials that this projection may be optimistic, especially if the security situation does not improve," Sopko wrote.

USAID told SIGAR it plans to try using third-party monitors of its project contractors, a plan the inspector general said it will investigate to be sure it actually works.

A spokesman for the State Department said officials there are exploring how to grow oversight bubbles by periodically sending security and medical personnel to the edges of accessible regions.

"Even if these alternative means are used to oversee reconstruction sites, direct oversight of reconstruction programs in much of Afghanistan will become prohibitively hazardous or impossible as U.S. military units are withdrawn, coalition bases are closed, and civilian reconstruction offices in the field are closed," Sopko said.

The IG asked each agency to respond with details about its plans for post-drawdown oversight, including information on lessons from Iraq and Pakistan the agencies can apply to Afghanistan; how many major projects, costing more than $5 million, they will have outside safe areas; and their specific plans for monitoring those projects and any third-party oversight personnel they use.