This is the first time I have heard anyone from the Pentagon confirm the number of Ground Based Interceptors currently fielded:

The United States has 30 ground-based interceptors targeting missiles from North Korea, Secretary of Defense Robert Gates said Thursday, according to Yonhap News.

“The advice that I got is, first of all, that system really is only capable against North Korea, and that 30 interceptors at the level of capability that North Korea has now and is likely to have for some years to come, 30 interceptors in fact provide a strong defense against North Korea in this respect,” Gates told a Senate Armed Services Committee hearing.

He was explaining the Barack Obama administration’s plans to cut back the budget for an increase of the interceptors to 44. “The decision not to go to 44 interceptors at this point does not mean we’ll never go to 44 interceptors, or at least more than 30,” he said. “It’s just that, over the period of the next few years, we don’t see the need to go to the additional interceptors, given the pace at which North Korea is developing its program.”  [Korea Herald]

Keep in mind that the US still has THAAD and AEGIS SM-3 to additionally defend against any North Korean missile attack.

If you haven’t already, I highly recommend reading my prior posting on Secretary Gates so called missile defense cuts.