Recognizing the difficulty of embarking on a third war, President Obama nonetheless said that the United States will participate in enforcing the U.N. Security Council resolution offering protection to Libya's citizens.
"Action is necessary and we will not be acting alone," Obama said.
The president spoke after meeting with congressional leaders in person and on the phone. He announced that Secretary of State Hillary Clinton will attend the Paris summit being convened Saturday by French President Nicolas Sarkozy.
That meeting will be attended by top leaders from Britain, the Arab League and other countries that will carry out the no-fly zone approved by the U.N. Security Council on Thursday.
Obama was careful to stress the leadership role being taken by other nations. But he emphasized that the "path of brutal suppression" taken by Libyan leader Moammar Gadhafi could not be allowed to stand unchallenged.
"For decades, he's demonstrated his willingness to use brute force," Obama said. "Here's why this matters to us: Left unchecked, we have every reason to believe Gadhafi would commit atrocities against his own people. Many thousands could die."
Obama's statement reflected the skepticism Western leaders had expressed all day about the Gadhafi regime's sincerity in declaring an "immediate cease-fire."
"We are so used to these hectic, contradictory statements issued by Tripoli several times a day for so long now that we don't believe them," French government spokesman Bernard Valero said.
Fighting was reported Friday in at least two Libyan cities, leaving Western and Arab nations to continue their preparations for military action.
In a joint statement to Gadhafi late Friday, the United States, Britain and France — backed by unspecified Arab countries — said a cease-fire must begin "immediately" in Libya, the French presidential palace said.
The statement called on Gadhafi to end his troops' advance toward Benghazi, the rebel headquarters, and pull them out of the cities of Misrata, Ajdabiya and Zawiya, and called for the restoration of water, electricity and gas services in all areas. It said Libyans must be able to receive humanitarian aid or the "international community will make him suffer the consequences" with military action.
Rebel leaders fighting to push Gadhafi from power said there was no cease-fire they could see. Cities like Misrata and Ajdabiya, they said, were still being shelled — claims the government denied.
A YouTube video posted Friday purported to show Misrata still under attack. The government has been trying for several weeks to retake the coastal city, a few hours from Tripoli. While there was no way to confirm the events independently, the TV network Al-Jazeera reported that Misrata was still being targeted.
In Washington, meanwhile, a Pentagon official told NPR the U.S. saw surveillance suggesting Libya's military was still active, firing on areas around Benghazi.
Caught By Surprise
It was not immediately clear whether the Gadhafi regime was seeking to buy time by eliminating the conditions that would authorize use of outside force under the terms of the Security Council resolution.
The Libyan regime will have to be judged by its deeds, not its words, British Prime Minister David Cameron told the BBC. French officials said that the facts on the ground have not changed.
The Security Council resolution was approved late Thursday with the backing of the United States, France and Britain, hours after Gadhafi vowed to launch a final assault and crush the nearly five-week-old rebellion against him.
A large crowd in Benghazi watching the vote on an outdoor projection TV burst into cheers, with green and red fireworks exploding overhead. In Tobruk, east of Benghazi, Libyans fired weapons in the air to celebrate the vote.
The Libyan regime appeared to have been caught by surprise by the speed with which the resolution was approved after weeks of discussion.
"As always, the regime was not very good at reading signals," says Dirk Vandewalle, a Dartmouth College government professor. "They should have started worrying as soon as the Arab League decided to support intervention."
Cameron told the British Parliament on Friday that he would send Typhoon and Tornado fighter jets to bases where attacks could be launched against Libya "in the coming hours."
The purpose of the no-fly zone would be to stop Gadhafi from launching "a brutal attack using air, land and sea forces" on the rebel stronghold of Benghazi, not to choose a government for Libya.
The former head of the British army, Richard Dannatt, said it was crucial to proceed cautiously "so we don't get into the kind of situation that we got into in Iraq by not having a Plan B for the morning after."
U.S. officials including Defense Secretary Robert Gates and Secretary of State Hillary Clinton had been wary of the no-fly zone resolution precisely because of the difficulty of limiting the Western mission once it gets under way.
"This resolution is an important step, but the U.S. and its partners will continue to explore other ways of ending the Libyan crisis," Clinton said Friday.
'A Slippery Slope'
Gates is scheduled to travel Saturday to Russia, which abstained from voting on the Security Council resolution.
There will be tensions between leaders who want to limit involvement to protecting rebels from the air and those who want to take Gadhafi out.
"It truly is a slippery slope," says Vandewalle, the Libya expert at Dartmouth.
"You either go in and finish your job, or you don't go in," he says. "Otherwise, you're going to have a war of attrition going on for quite some time, with occasional bombing from the Western powers."
Those Western powers faced pressure to act urgently after weeks spent deliberating over what to do about Gadhafi as his regime gained momentum.
"Things really came together quickly at the end," NPR's David Greene said Friday on Morning Edition. "There was a sense for days that this might never happen, the debate might continue.
"All sides said the support from the Arab League and potentially the willingness of Arab countries to take part in this lent that final needed support to push this through," said Greene, who was reporting from Tripoli.
Obama telephoned the leaders of Britain and France after the vote, the White House said. U.S. officials speaking after a closed-door briefing in Congress said the attempt to ground Gadhafi's air force could begin by Sunday or Monday with the use of jet fighters, bombers and surveillance aircraft.
Gadhafi, calling in to Libyan television on Thursday, said his forces would "rescue" the people of Benghazi, the eastern Mediterranean port city that has become the de facto rebel capital and staging ground. For those who resist, Gadhafi said, there would be "no mercy or compassion."
"This is your happy day, we will destroy your enemies," he said, warning the people of Benghazi not to stand alongside the opposition. "Prepare for this moment to get rid of the traitors. Tomorrow we will show the world, to see if the city is one of traitors or heroes."
Gadhafi also pledged to respond harshly to U.N.-sponsored attacks in an interview with Portuguese television broadcast just before the vote. "If the world is crazy," he said, "we will be crazy, too."
In central Tripoli on Friday, Sirhan Firage, 33, said the reports of other countries getting ready to attack Libya unnerved her.
"I'm worried for my country. ... Even [though I am a woman], if they attack us I will go and defend my country," she said.
Firage said she's convinced the Security Council made its decision to intervene in Libya based on lies.
There are "false accusations that our leader is killing us," she said, "but I want to say a word to the whole world: If Gadhafi wanted to kill us, we will accept it. But we will never accept a foreigner coming kill us. In fact, no father [would] kill his children. We are his, Gadhafi's children. We do not trust the foreigners."
Europe's air traffic control agency, Eurocontrol, said Friday that "the latest information from Malta indicates that Tripoli [air control center] does not accept traffic."
The Brussels-based agency had no information on how long Libya's airspace would be closed but said it had halted all air traffic to Libya for 24 hours.
Libyan Deputy Foreign Minister Khaled Kaim struck a more conciliatory tone, offering to negotiate a cease-fire with the rebels. He welcomed the Security Council's concern for the people of Libya but called on the world not to allow them to receive weapons. "If any countries do that, they will be inviting Libyans to kill each other," he said.
In Tripoli on Friday, foreign journalists were barred from leaving their hotel. "It's been a crazy night in Tripoli," Greene reported.
The shift toward international action reflected dramatic change on the ground in Libya in the past week. The rebels, once confident, found themselves in danger of being crushed by an overpowering pro-Gadhafi force using rockets, artillery, tanks and warplanes. That force has advanced along the Mediterranean coast aiming to recapture the rebel-held eastern half of Libya.
Gadhafi troops encircled the city of Ajdabiya, the first in the path of their march, but also had some troops positioned beyond it toward Benghazi.
The unrest in Libya began Feb. 15 in the eastern city of Benghazi and spread east to Tripoli, the capital. Like others in the Mideast, the protest started with popular demonstrations against Gadhafi, rejecting his four decades of despotic and often brutal rule. The tone quickly changed after Gadhafi's security in Tripoli forcefully put down the gatherings there.
Soon rebel forces began arming themselves, quickly taking control of the country's east, basing themselves in Benghazi, the second-largest Libyan city, with a population of about 700,000. Some Libyan army units joined the rebels, providing them with some firepower, but much less than Gadhafi's remaining forces and, crucially, no air power.
There are no official death tolls. Rebels say more than 1,000 people have been killed in a month of fighting, while Gadhafi claims the toll is only 150.
With reporting from NPR's David Greene in Tripoli, Eleanor Beardsley in Paris and Alan Greenblatt. Material from The Associated Press was used in this report.