Is the US government tracking near-Earth objects (NEOs)? NASA says yes:
In terms of the discovery efforts for NEOs, NASA's current goal is to discover at least 90% of all NEOs whose diameters are larger than 1 kilometer within 10 years. To meet the NASA goal, the rate with which new objects are discovered will necessarily be largest in the first few years. This is because during the latter years of the 10-year interval, more and more "discoveries" will actually be of objects that have been previously found. Currently, the best estimate of the total population of NEOs larger than one kilometer is about 1000. The progress toward discovering 90% of this population can be monitored under the web page entitled Number of NEOs within the section on Near-Earth Objects.Do we have a ready-to-go plan for objects that could do catastrophic damage? Er, not yet. From a report to NASA's Office of the Chief Technologist:
Despite the lack of a known immediate threat from a near-Earth object (NEO) impact, historical scientific evidence suggests that the potential for a major catastrophe created by an NEO impacting Earth is very real. It is only a matter of when, and humankind must be prepared for it. During the past two decades, various concepts and techniques for mitigating the impact threats from NEOs have been proposed. Unfortunately, many of these previously proposed concepts were impractical and not technically credible. In particular, all non-nuclear techniques, including slow-pull gravity tractors and kinetic-energy impactors, require mission lead times much larger than 10 years, even for a relatively small NEO. However, for the most probable impact threat with a warning time less than 10 years, the use of high-energy nuclear explosives in space becomes inevitable for proper fragmentation and dispersion of an NEO in a collision course with the Earth. However, the existing nuclear subsurface penetrator technology limits the impact velocity to less than 300 m/s because higher impact velocities destroy prematurely the detonation electronic equipment. Thus, an innovative space system architecture utilizing high-energy nuclear explosives must be developed for a worst-case intercept mission resulting in relative closing velocities as high as 5-30 km/s.What if a near-Earth object actually hits the United States? Is the Federal Emergency Management Agency ready? A 2001 report by a pair of scientists is not reassuring:
We have little idea about the role that a civilian agency like FEMA might play in the NEO hazard (it has so far given essentially zero consideration to the issue at all). We know even less about the analogous entities in other countries as well as international entities that similarly need to be informed about this issue.