Should the White House defend "Targeted Killings"

According to this report, "[t]he Obama administration sought Friday to block a lawsuit over the scope of its targeted killing program for suspected terrorists, in a case that challenges the government to define the limits of its global battlefield against extremists."  Let's put aside, for now, reactions of the "gee, this wasn't supposed to happen under the Obama Administration" or "Imagine if President Bush did this, how people would howl!" variety.  (Oops.)   I want to ask, instead, whether or not is clear that "targeted", extrajudicial killings are morally unjustifiable.

I take it that, for those of us who think that capital punishment is morally justifiable, it is clear that targeted, extrajudicial killings are morally unjustifiable as punishment.  But, does it follow that it is always unjustifable for the government to authorize, outside of judicial processes, the killing of a person who is thought (with certainty, or something close to it?) to pose an imminent threat to the safety of others?  Does the "distance" between the decision maker and the supposed-soon-to-be aggressor matter?  Or, does the question reduce to the more familiar one about when lethal force is permissible in defense of self or others?  Or, instead, to the question when it is permissible to kill a combatant (notwithstanding the fact that the decision-maker and the supposed-aggressor are not meeting on a "battlefield")?

Thoughts?