In contrast to NASA's reluctance to step outside manned and robotic exploration, DOD has long had voices calling it to take leadership in Planetary Defense:
From as far back as Feb 2000:
A high-ranking U.S. Military official -- speaking in a non-official capacity -- says the hunt for potentially Earth-threatening space rocks should be more centralized, and the Department of Defense could be a primary force behind this project.
Pete Worden, deputy director for Command and Control at the U.S. Air Force Headquarters in the Pentagon, suggested an array of micro-satellites should be used to find and study Near Earth Objects -- asteroids and comets known as NEOs -- in an effort to save money and speed up the search process.
And even before that in:
France Article (Contains specific Legislative proposals):
Other links of interest:
Report to congress:
AOA behind the Report as posted by NASA:
AOA behind the report as posted by B612 Foundation
Know what to do, don't have the Money:
http://www.signonsandiego.com/news/science/20070305-1432-killerasteroids.html AIAA Position Paper: