Officials, saying international support could come from regional blocs, noted that NATO’s air attacks on Serbia in 1999 came without U.N. backing.

“If you have [support from] the Arab League, the African Union, NATO and potentially the European Union, you have every country within 5,000 miles of Libya,” a NATO official said. “That gives you a certain level of legitimacy.”…

As they weighed the prospect of intervention, the Obama administration and European governments continued efforts to size up the Libyan opposition. “We feel that we don’t really understand who they are yet,” said a senior European diplomat who, like other officials interviewed, spoke on the condition of anonymity to discuss closely held deliberations. “They are more fractured and complicated and less well-coordinated than we would like.”