UNITED NATIONS >> The United States and its allies are looking beyond the painfully divided U.N. Security Council to legitimize military action against Syria, trying to build a cohesive rationale for a strike and win broad international backing.

The United States, Britain and France have made it clear they believe the government of Syrian President Bashar Assad was behind a recent deadly chemical weapons attack in the suburbs of Damascus, and that such an act demands a swift international response.

That would almost certainly require acting without the approval of the council, where Russia and China have consistently used their veto-power to deflect a strong response to the 2  1/2-year-old Syrian conflict. It also could mean acting well before a team of U.N. chemical weapons inspectors now in Syria delivers an assessment on whether such an attack occurred.  

The task at hand for any U.S.-led coalition will be to win the support of key international organizations outside the United Nations.

One path may be persuading NATO to get involved or even lead any military action. That helped the Clinton administration cast a frame of legitimacy on the Kosovo war in the late 1990s even though the Security Council, with Russia firmly opposed, never sanctioned the bombing campaign against Belgrade, said Ken Pollack, an expert on Middle Eastern political-military affairs at the Brookings Institute.

“Very famously, the Kosovo war was not legal,” Pollack said. “Yet … you don’t have people running around screaming that the Kosovo war was illegal. That is because the U.S. did a good job of building a case for it.”

A U.S.-led coalition is likely to invoke an international doctrine known as the Responsibility to Protect, which states that the international community has an obligation to act to prevent crimes against humanity no matter where they occur, said Stephen Biddle, an expert on U.S. military and foreign policy at George Washington University. Biddle noted that the doctrine is increasingly perceived as superceding the need to respect a country’s sovereignty.

“The two natural avenues are NATO and the doctrine of responsibility to protect,” he said.

The push for international support got a boost today when the Arab League appeared to support military action, placing the blame for the alleged chemical weapons attack squarely on the Assad regime and urging the Security Council to agree on “deterrent” measures against those who committed “this heinous crime.”

The call, which came at an emergency meeting, followed multiple conversations between U.S. Secretary of State John Kerry and key Arab counterparts among others. The State Department said Kerry spoke twice on Monday with both the foreign minister of Jordan and the Arab League secretary general, as well as once each with the foreign ministers of Saudi Arabia, the United Arab Emirates, Qatar, Turkey and Britain.

Kerry also spoke with U.N. Secretary General Ban Ki-moon, European Union foreign policy chief Catherine Ashton and NATO Secretary General Anders Fogh Rasmussen, the State Department said.

With little appetite among Americans for plunging into another Mideast conflict, the Obama administration cast its rationale for striking Syria in narrow terms. The goal would not be regime change — as was the case in Iraq — but punishing Syria for its violations of international treaties on chemical weapons, White House spokesman Jay Carney said.

U.N. spokesman Farhan Haq said today that U.N. Secretary General Ban Ki-moon’s stance remains unchanged: “Our focus is away from any military solution and toward a diplomatic solution.”

But the United States, France and Britain all argued this week that waiting for U.N. action can no longer be justified.

French President Francois Hollande suggested that the Security Council’s failure to act so far is justifying a terrible international crime.

“International law must evolve with the times. It cannot be a pretext to allow mass massacres to be perpetrated,” French President Francois Holland said today. He then went on to invoke France’s recognition of “the responsibility to protect civilian populations” that the U.N. General Assembly approved in 2005.

Obtaining NATO involvement is not a given: the military coalition requires consensus for such action and there were signs of reluctance.  Ashton, the EU foreign policy chief, said the support of the Security Council for the use of force against Syria remains “extremely important.” Italy echoed that stance. Turkey indicated it would take part in an international coalition against Assad’s regime — if the U.N. failed to come up with sanctions to punish Syria for the alleged use of chemical weapons.

That raises the question of whether the U.S. and its allies, if they decide to go through with a military strike, should attempt to seek Security Council approval at all. Pollack said forcing to the Russians and the Chinese to vote “no” might help persuade reluctant countries. “You demonstrated that you tried and hopefully isolate the Russians in doing that,” he said. On the other hand, if too many Security Council members join the “no” vote, it could undermine the impression of a strong international backing.

“It could be embarrassing,” Pollack said.