The Arab League endorsed the imposition of a no-fly zone over Libya on Saturday and recognized the fledgling rebel movement seeking to topple Libyan leader Moammar Gaddafi as the country’s legitimate government, increasing pressure on Western powers to intervene in what increasingly resembles a civil war.

The move represents an extraordinary step by the leading Arab organization, historically reluctant to sanction a member, and provided fresh evidence of the reformist spirit recasting long-stagnating Arab politics. It was also a risky step for a number of Arab leaders facing domestic dissent of their own.

The vote significantly ratchets up pressure on the Obama administration and its European allies to act on behalf of Libya’s rebels, who are under heavy assault from Gaddafi’s far better-armed forces. NATO has called Arab League support a precondition for military action in Libya, and the Saturday vote gave new momentum to proposals for a protective no-fly zone over the oil-rich country.

“The main priority right now is to stop the deadly situation,” said Amr Moussa, the Arab League’s secretary general, in announcing the decision after 51 / 2 hours of closed-door deliberations.

The Arab League acted on the eve of a potentially decisive week of international diplomacy surrounding events in Libya, and the White House welcomed the vote in a short statement.

“The international community is unified in sending a clear message that the violence in Libya must stop, and that the Gaddafi regime must be held accountable,” the statement said. “The United States will continue to advance our efforts to pressure Gaddafi, to support the Libyan opposition, and to prepare for all contingencies, in close coordination with our international partners.”

Secretary of State Hillary Rodham Clinton travels to the region Monday for meetings with representatives of the rebels’ provisional government, the National Transitional Council, based in the eastern city of Benghazi. NATO officials will meet midweek to consider a no-fly-zone proposal, as France and Britain draft a resolution authorizing the mission for possible U.N. Security Council review.

The Arab League vote called on the Security Council to approve the no-fly zone as quickly as possible. But the Obama administration, which is already fighting two wars in Muslim countries, faces a number of issues in Libya that complicate any military intervention.

The administration knows little about Libya’s rebels or what kind of government would replace Gaddafi’s erratic 41-year-long rule. It also has to contend with a de facto civil war on the ground that makes intervention more urgent and complex by the day.

Purpose still debated

Military analysts differ on whether a no-fly zone would significantly change the balance of power in Libya, now shifting swiftly toward Gaddafi’s forces. Much of the fighting is being done by ground forces, including tank-fired artillery, but the government has used air power to bomb rebel positions.

Adopting the recommendation of a no-fly zone, however, would probably send a message to Gaddafi and his inner circle, that the United States and its European allies intend to intensify pressure to achieve their declared goal of ousting the Libyan leader.

Conservatives and liberal interventionists are growing increasingly vocal about what they deem the need for a no-fly zone to ensure that Gaddafi does not remain in power. At a Friday news conference, Obama said that “we’re going to take a wide range of actions to try to bring about that outcome.”

“It is vital to everything that Obama is trying to achieve in the region that we be able to say when this is over that Gaddafi failed,” said Tom Malinowski, the Washington director of Human Rights Watch, adding that the Arab League vote will make it easier for the administration to move ahead with a no-fly zone.

“Otherwise, the conclusion other authoritarian governments will draw is that [toppled Egyptian president] Hosni Mubarak made a mistake not massacring the protesters in Tahrir Square, and that Gaddafi’s survival strategy is the one to emulate,” Malinowski continued. “We need to be able to say that Gaddafi used violence and failed, and that others in the region, whether the king of Morocco or crown prince of Bahrain, accepted peaceful change and succeeded.”

Europe taking the lead

Obama has been willing to let European allies publicly lead the search for solutions in Libya, in part to allow regional bodies such as the Arab League more political room to move against Gaddafi.

Mindful of the low Arab public opinion of the United States, Obama and his advisers have concluded that Arab leaders would find it harder to support international sanctions or military operations against Libya if Washington was calling loudest for them.

European leaders, particularly French President Nicolas Sarkozy, have spoken far more boldly about military action in Libya than Obama, whom conservatives have accused of being absent at a time of historic change in the strategically important region.

Officials of Libya’s government-in-waiting welcomed the Arab League’s endorsement of a no-fly zone and said they hoped the United States and other Western powers would follow suit.

“We hope the Europeans will deliver now. This changes things a lot,” said Mustafa Gheriani, a spokesman for the National Transitional Council. “We hope it will change the American position, but most of all the European position.”

Abdul Hafidh Ghoga, the council’s vice chairman, said that if a no-fly zone is imposed, the rebels will “prevail” over Gaddafi’s forces. But he warned that if Western powers do not take military action, the rebels are prepared to buy weapons from other countries to protect the revolution.

“If the international community chooses to play the role of bystander, with Libyan cities being destroyed and Libyan people being killed, then we will have to defend ourselves on our own,” Ghoga said. “If no steps are taken, we have to take the decision to arm ourselves as best as we can.”

‘Humanitarian action’

In announcing the Arab League’s decision, Moussa described the no fly-zone as a “preventive measure” whose chief goal is to “protect Libyan citizens.”

The vote was taken by the foreign ministers of 21 Arab nations. Representatives of Gaddafi’s government, which the league suspended as a member this month, were not invited.

Addressing a packed news conference, Moussa said the Arab League would begin working at once with the Libyan provisional government. He referred to a section of the statement, issued after the vote, that condemned “the fatal violations and serious crimes at the hands of Libyan authorities” in declaring Gaddafi’s regime illegitimate.

But Moussa, who is seeking to replace Mubarak in future elections, avoided describing the no-fly zone in military terms. He called the vote an endorsement of a “humanitarian action.”

With popular revolutions and anti-government demonstrations underway from the Persian Gulf to Morocco, the vote amounted to a risky, potentially precedent-setting move by the aging monarchies and brittle autocracies that have run the region for years.

The Arab government of Sudan, for example, has carried out a brutal campaign against Africans in the western Darfur region, and anti-genocide groups have for years called for a no-fly zone to protect them. Jordan, Bahrain, Yemen and other member countries are confronting varying degrees of unrest.

Outside the league’s headquarters on Tahrir Square, Egyptians and Libyans waved signs describing Gaddafi as a genocidal butcher and displayed photographs of dead Libyans.

But they also expressed wariness over the potential for Western military involvement in the conflict, highlighting the diplomatic balancing act the Obama administration and its allies are attempting to strike.

“We are not calling for American intervention,” said Omar Mohamed, a 21-year-old student. “But they should give weapons to the rebel fighters.”

Wilson reported from Washington. Correspondent Sudarsan Raghavan in Benghazi, Libya, and staff writer Peter Finn in Washington contributed to this report.