Obama: U.S. Involvement in Libya Action Would Last 'Days, Not Weeks' U.S. president tells Libyan leader to stop violence or face military action.

March 18, 2011 -- President Obama told a bipartisan group of members of Congress today that he expects the U.S. would be actively involved in any military action against Libya for "days, not weeks," after which he said the U.S. would take more of a supporting role, sources tell ABC News.

The White House meeting with 18 lawmakers came as Obama delivered an ultimatum to Libyan leader Moammar Gadhafi that he must immediately implement a ceasefire in all parts of Libya and allow international humanitarian assistance, or risk military action against his regime.

"Moammar Gadhafi has a choice. The [U.N.] resolution that passed lays out very clear conditions that must be met. The United States, the United Kingdom, France and Arab states agree that a ceasefire must be implemented immediately. That means all attacks against civilians must stop," the president said today. "Humanitarian assistance must be allowed to reach the people of Libya."

"These terms are not subject to negotiation," Obama said. "If Gadhafi does not comply with the resolution, the international community will impose consequences and the resolution will be enforced through military action."

Sources told ABC News that Obama's decision to support the use of force came Tuesday, following several days of internal administration deliberations and the realization that diplomatic efforts to stop the brutality of Gadhafi's regime weren't working.

Presented with intelligence about the push of the Gadhafi regime to the rebel stronghold of Benghazi, the president told his national security team, "What we're doing isn't stopping him."

Some in his administration, such as Secretary of State Hillary Clinton, had been pushing for stronger action, but it wasn't until Tuesday, administration sources tell ABC News, that the president became convinced sanctions and the threat of a no-fly zone wouldn't be enough.

Obama's speech Friday indicated that coalition forces are giving Gadhafi time to change course, but are also gearing up for an attack if their demands are not met.

He also reiterated that the potential conflict was international in form, saying that any action in Libya would be led by European and Arab forces, and that no ground troops will be deployed.

"We are not going to use force to go beyond a well-defined goal, specifically the protection of civilians in Libya," he said.

The president is mindful that the American public is weary of war, and that the world community casts a skeptical eye at American plans to take military action against yet another Muslim country. Obama has tried hard not to feed into Gadhafi's megalomaniacal worldview by making this confrontation about him versus Obama, or the United States versus Gadhafi, officials say.

The United States has very much been leading the charge behind the scenes, but the White House has deferred public action to the State Department and the United Nations. The administration has also worked furiously to put a European and Arab face on the opposition to Gadhafi's action.

On Saturday, France will host a high level meeting of representatives from the Arab League and European Union to discuss the implementation of the no-fly zone or targeted strikes inside Libya. Secretary of State Hillary Clinton will also attend.

World Preparing for Military Action Against Libya

French President Nicolas Sarkozy will meet with the Emir of Qatar Saturday. Qatar and the UAE, and possibly Jordan, are expected to lend their jets to any military action. A European diplomat said that barring major developments on the ground prior to the meeting, there likely won't be any military action before then.

Gadhafi's regime, faced with U.N.-backed airstrikes, declared a ceasefire today as Libyan forces menaced the rebel capital of Benghazi.

The country's foreign minister said Libya accepted the United Nations Security Council resolution and had implemented a ceasefire. But there were reports of ongoing fighting and shelling in Misurata, an indication that the promise may not be in effect or not applied to all of Libya.

International military action against Libya could begin soon, but concerns about such an action remain high.

Most of Libya's air defenses are in the western part of the country, around the capital of Tripoli. The main military threat is in the east, where rebels have ascended to power, but even in the east there is a danger of man portable air defenses (MANPADS) or shoulder-fired missiles. There are hundreds of them, and there's not much that the international coalition can do about it because they can't be tracked.

Clinton said that the United States will continue to work with the international community to press Gadhafi to leave, but warned that it's too soon to tell what the final outcome might be.

"We do believe that a final result of any negotiations would have to be the decision by Col. Gadhafi to leave. But let's take this one step at a time," Clinton said. "Until we can have a better idea of what actually happened, it's hard to know what the next steps will be."

The U.N. approved a resolution late Thursday authorizing the international community to take "all necessary measures," short of sending in ground troops, to protect civilians in Libya, and to impose a no-fly zone. The resolution does not authorize taking out Gadhafi or regime change.

The Libyan government closed its air space to traffic following the vote.

Prior to the vote, Gadhafi gave an interview to a Portuguese television station assailing the U.N. and vowing that Libya would retaliate strongly if the resolution were to pass.

"According to the U.N. Charter, the Security Council has no right to intervene in the internal affairs of any state," Gadhafi said. "We'll answer them, our response will make their lives hell as well, as they are making our lives hell. They will never enjoy peace because this is injustice, unfairness."

The world jumped into the conflict just as Gadhafi's forces threatened to attack the rebel stronghold of Benghazi in eastern Libya.

The longtime dictator issued a warning to the residents of Benghazi Thursday. "We are coming tonight," he said. "There won't be any mercy."

Gadhafi and his supporters remain defiant.

Gadhafi's son, Saif, told ABC News via a phone interview that the U.N. resolution is a "big mistake" and that if the United States wants to help, they should in fact help the government.

"We want to live in peace, so we want even Americans to help us get rid of the remnants of those people and to have a peaceful country, more democratic," he said. "If you want to help us, help us to, you know, to be democracy, more freedom, peaceful, not to threaten us with air strikes. We will not be afraid. Come on!"

No-Fly Zone Will Take Time

It would not be difficult for the international community to establish a no-fly zone, but the main question is whether forces would intervene just to prevent a slaughter in Benghazi or to ouster Gadhafi.

U.S. Air Force Chief of Staff Gen. Norman Schwartz said Thursday it could take upwards of a week to fully establish a no-fly zone and that public comments by some that it could be done in a few days are "overly optimistic."

He acknowledged there are limited Air Force assets because most of them are in Iraq and Afghanistan, especially transport aircraft.

Last week, Department of National Intelligence director James Clapper said the Libyan air force was large in raw numbers, but only a small number of aircraft were actually flying. A Pentagon analysis of Libya's air capabilities shows the overall readiness of Libyan aircraft is poor by western standards and most aircraft are now dated or obsolete in terms of avionics or upgrades. Eighty percent of the air force is judged to be "non-operational and "overhaul and combat repair capability is also limited."

ABC News' Christiane Amanpour, Kirit Radia and Luis Martinez contributed to this report.