As the campaign evolves, officials said, U.S. support aircraft would provide airborne surveillance, refueling and radar-jamming capabilities, and several F-16s may participate in patrols over no-fly zones above Tripoli and Benghazi.
In an audio statement broadcast on Libyan state TV, Gadhafi called the attacks a "crusade" against the Libyan people and called on Arab countries and African allies to come to his government's aid.
"We ask others to stand by us," he said, according to a translation of his remarks heard on Al Jazeera. "We must now open the weapons depot and arms to all Libyans."
Gadhafi warned the international coalition Friday not to interfere in Libyan affairs, calling the U.N. resolution "invalid" and appealing directly to world leaders, including President Obama, in a letter.
"Libya is not yours. Libya is for the Libyans," he said in the letter. "If you had found them taking over American cities with armed force, tell me what you would do."
Military action in Libya follows weeks of intensive, international diplomatic pressure on Gadhafi to cease the violence and pull back from rebel-held cities.
The Security Council 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 [U.N.] resolution that passed lays out very clear conditions that must be met," Obama said Friday.
"These terms are not subject to negotiation. If Gadhafi does not comply with the resolution, the international community will impose consequences and the resolution will be enforced through military action," he said.
Exactly what role the U.S. military would play in enforcement of the resolution remains unclear.
"We will support an international coalition as it takes all necessary measures to enforce the terms of resolution 1973," Secretary of State Clinton said today in Paris.
But Clinton declined to detail U.S. responsibilities in a supporting an attack, other than to say that the United States would offer "unique capabilities." She emphasized that the United States will not deploy ground troops in Libya.
During a meeting with a bipartisan group of members of Congress Friday, Obama said he expects active U.S. involvement in any military action would last just "days, not weeks," sources told ABC News.
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 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.
"We are not going to use force to go beyond a well-defined goal, specifically the protection of civilians in Libya," Obama said Friday.