Robert Gates, the US Secretary of Defense, just said that Obama has authorized the use of of Predator Drones in Libya against Gaddafi's forces. In fact, the first mission of the Predator Drones in Libya had taken place earlier this week.
They've already used drones for gathering intelligence in Libya, but sending in Drones armed with Hellfire missiles would mark a significant growth in USA's contribution to the now NATO led effort in Libya. These unmanned predator drones pack a punch but more importantly mean that by sending these drones, USA is not sending its troops there. Hopefully, that won't change.