Private contractors will make up at least half of the total military workforce in Afghanistan going forward, according to Defense Department officials cited in a new congressional study.

As President Obama's escalation of the war in Afghanistan unfolds, the number of contractors will likely jump by between 16,000 and 56,000, adding up to a total of 120,000-160,000, according to an updated study from the Congressional Research Service.

DOD officials who spoke with the study's author said contractors would make up 50-55 percent of the total workforce -- troops plus contractors -- in the future. This would actually be a significant reduction from the last two years, when contractors have averaged 62 percent of the total.

As we've reported, many questions about the army of contractors, which outnumbers the size of the U.S. troop force, remain unanswered and underexamined. We don't have up to date numbers on how much the United States spends on private contracts, and the DOD does not break down the services done by contractors in Afghanistan (it does for Iraq).

As of September 2009, contractors providing security, transportation, and logistical services numbered 104,100 in Afghanistan and 113,700 in Iraq, according to the military. Most of the contractors in Afghanistan are local nationals, according to the military. Here's a table looking at how much the numbers in Afghanistan will increase with Obama's surge:

Interestingly, it looks like military planners themselves -- not just the media and politicians -- find it all too easy to ignore the role of contractors in U.S. foreign policy. The most recent Quadrennial Defense Review, a key strategic overview of American defense and military policy, runs over 100 pages. Just five sentences of the QDR document addresses the use of private contractors, the CRS study notes.

Besides crunching the numbers, the study also looks at whether contractors can undermine U.S. efforts in Iraq and Afghanistan, including the issue of abuses of civilians by contractors.

Here's a graph we've shown you before, now updated through September 2009:

The whole study is worth a read:

CRS Contractors Study 12/09