The appropriate comparison is Bosnia or Kosovo, or even Rwanda where a massacre is unfolding on live television and the world is challenged to act. It is time for the United States, NATO, the United Nations and the Arab League to act forcefully to try to prevent the already bloody situation from degenerating into something much worse.
By acting, I mean a response sufficiently forceful and direct to deter or prevent the Libyan regime from using its military resources to butcher its opponents. I have already seen reports that NATO has sternly warned Libya against further violence against its people. Making that credible could mean the declaration and enforcement of a no-fly zone over Libya, presumably by NATO, to prevent the use of military aircraft against the protesters. It could also mean a clear declaration that members of the regime and military will be held individually responsible for any future deaths. The U.S. should call for an urgent, immediate Security Council meeting and push for a strong resolution condemning Libya's use of violence and authorizing targeted sanctions against the regime. Such steps could stand a chance of reversing the course of a rapidly deteriorating situation. An effective international response could not only save many Libyan lives, it might also send a powerful warning to other Arab leaders who might contemplate following suit against their own protest movements.
Andrew Sullivan has an interesting roundup of ideas on this question.