The US seems to have been almost completely impotent on this one. Cameron started the charge before losing his nerve, and Sarko took it to the breach. Hill and Obama picked at their cuffs until the AU kissed their booty hard enough to let Sarko and Cameron off the leash.
This would have been awesome two weeks ago, now its a bit to little to late I am afraid. The funny thing is that there is no real difference in the reasons to come to this course of action than there was then, all we needed is one particular person to have taken this leadership opportunity to do something that was a no brainer.
Maintaining a pretence of US non-involvement (or at least, maintaining a pretence that it isn't a US led effort) is pretty important for the US. That they waited for multilateral approval, and that they will not lead enforcement are most likely calculated decisions, not a lack of leadership.
Although it would've been nice to see faster movement towards this.
Also, a victory for the UN (it can do something!).