President Obama is sending his secretary of state to Paris tomorrow for a key meeting of European and Arab leaders that will seek to define the terms of military engagement in Libya against Muammar Qaddafi’s military.

Secretary Hillary Clinton has been a strong advocate for a no-fly zone, and during a trip to Arab states this week she called for attacks on Libyan military sites and for Colonel Qaddafi's departure.

The Paris meeting will come two days after the United Nations Security Council passed a resolution allowing “all necessary measures” against Qaddafi's forces, which have been making gains on the rebel fighters and approaching the de-facto opposition capital Benghazi. On Friday, Qaddafi's government declared a cease-fire even as its attacks continued on rebel holdouts.

The Paris meeting will center on two simple questions, says Antoine Sfeir, director of the Middle East Journal in Paris: “Are we going to protect the inhabitants of Benghazi physically, or not? Do we believe the cease-fire of Qaddafi, or not?”

Britain and France led the push for a UN resolution in an unusual moment of European resolve. French President Nicolas Sarkozy is hosting Saturday's meeting in Paris, which will include Britain’s David Cameron, Germany’s Angela Merkel, European Union foreign policy chief Catherine Ashton, UN Secretary General Ban Ki-moon, and leaders from the Arab League, the United Arab Emirates, Saudi Arabia, Iraq, and Qatar.

Along with discussing logistical details such as the scope of operations and potential military targets, the US and Europeans are expected to urge extensive participation from Arab nations and try to harmonize positions with the Arab League, whose original call for a no-fly zone was more limited than the UN resolution.

Arab League chief Amr Moussa said in Cairo today the European-led partnership against Libya should not “go too far” and not be an invasion. "The goal is to protect civilians first of all, and not to invade or occupy… The Arab League decision was clear, what we need is a no-fly zone and safe areas."

Resolution 1973 – which passed Thursday night with abstentions from Russia, China, Germany, and Brazil – calls on member states “to take all necessary measures … to protect civilians and civilian populated areas under threat of attack." It offers considerable room of interpretation.

In an apparent effort to further isolate Qaddafi, the International Criminal Court's chief prosecutor Luis Moreno-Ocampo said today that his investigation against Libyan officials may be completed by May, and would focus on individuals responsible for committing crimes against civilians but not on pilots carrying out the UN mandate.

French Foreign Minister Alain Juppé told reporters today that “everything is prepared” for military action Sunday. French officials earlier said their jets would take flight today. Britain's Prime Minister Cameron said the UK will deploy Tornado jets and Typhoon aircraft as well as refueling and surveillance aircraft.