WASHINGTON - President Obama is offering Congress and an anxious public his first detailed accounting of his rationale for U.S. military involvement in Libya and perhaps an answer to the burning question: What's next?
His speech, set for 7:30 p.m. EDT Monday, comes after the administration scored an important diplomatic victory. NATO ambassadors on Sunday approved a plan for the alliance to assume from the U.S. command of all aerial operations, including ground attacks.
As CBS News national security correspondent David Martin reports, the American military will remain indispensable to the success of Operation Odyssey Dawn -- the official name for the coalition military effort in Libya -- even as other NATO nations take the lead role.
But NATO's official takeover of the no-fly zone will help Mr. Obama assure the nation he can deliver on his promise that the United States will be a partner in the military action against Libya, but not from the driver's seat. Bickering among NATO members delayed the process.
Ahead of Monday's speech, Mr. Obama and his top national security officials worked to set the stage for the address Obama in his weekly radio and Internet address, and Secretary of State Hillary Rodham Clinton and Defense Secretary Robert Gates with appearances on Sunday television news shows.
But as they made the rounds, neither Clinton nor Gates could say how long the U.S. mission would last or lay out an exit strategy.
"I don't think anybody knows the answer to that," Gates told ABC News' "This Week" when asked pointedly about reports that some officials within the Pentagon believed the mission could last many months.
Clinton was asked on NBC's "Meet the Press" what would be an acceptable outcome given that Obama has both said that Libyan leader Col. Muammar Qaddafi must go and that he is not a military target. Would a partitioning of Libya be a possible solution? "I think it's too soon to predict," she said.
The interviews were conducted Saturday and aired Sunday.
CBS News senior White House correspondent Bill Plante reports that, according to administration sources, Mr. Obama will argue U.S. and allied intervention in Libya has not only averted a catastrophe, but also advanced American interests.
Plante says the President will likely point to this weekend's push westward toward the Libyan capital as evidence that the until-recently-U.S.-led coalition military effort is paying dividends. The area retaken accounts for a substantial chunk of Libya's 1.5 million barrels of daily oil exports -- which have all but stopped since the uprising began in mid-February.
The biggest challenge for President Obama, says CBS News political analyst John Dickerson, will be clearing painting the link between the immediate military goal of protecting Libyan civilians from attack by their own leader, and the secondary goal of ousting that leader.
Now that NATO has officially assumed the lead role militarily, says Dickerson, Mr. Obama will likely point to that success and ask the American people to trust his judgment on the decision of how much further U.S. help is warranted in achieving goal number two; removing Qaddafi.
His explanation is very unlikely to convince lawmakers who have smarted over Mr. Obama's move to involve the U.S. military without consulting them first, however, adds Dickerson. "If each case is decided on the merits at the time, what can they expect in future," members of the U.S. Congress might be left to wonder.
Mr. Obama's speech from the National Defense University in Washington comes as leading GOP lawmakers and some from within Mr. Obama's own party are pressing him for more clarity about his goals.
The President did not seek congressional authority before he took military action in Libya, nor did he consult closely with congressional leaders, sore points for lawmakers on both sides of the aisle.
Congress wants to know the precise U.S. military role in the days ahead and how a nation strained by two existing wars and mushrooming budget deficits can pay the tab.
"Who knows how long this goes on and, furthermore, who has budgeted for Libya at all?" said Indiana's Sen. Richard Lugar on NBC's "Meet the Press." Added Lugar, the senior Republican on the Senate Foreign Relations Committee: "I don't believe we should be engaged in a Libyan civil war. The fact is we don't have particular ties with anybody in the Libyan picture. It is not a vital interest to the United States."
Gates generally agreed that Libya did not pose a direct threat the U.S. "It was not a vital interest to the United States," he said, while suggesting that what happened there could have implications for democratic movements in other parts of the Middle East where the U.S. does have a more direct stake.
Mr. Obama asserted in his weekly address on Saturday that the U.S. mission was "clear and focused," is succeeding, has taken out Qaddafi's air defenses and has saved "the lives of countless citizens" who were threatened by Qaddafi.
On Monday night he will discuss how the mission advanced U.S interests, the White House said. He is also expected to reiterate that U.S. ground forces will not be put into Libya under any circumstance and that the United States will complete the transfer of its lead role to NATO and other partners.
That had always been Mr. Obama's plan, but it hit a snag amid feuding among some NATO members last week. Before Sunday's decision, NATO had only agreed to oversee enforcement of the no-fly zone. The new decision extends that authority to protecting from the air Libyan citizens being attacked or pursued on the ground by Qaddafi's forces.
"NATO allies have decided to take on the whole military operation in Libya under the U.N. Security Council resolution," Secretary-General Anders Fogh Rasmussen said in a statement. "NATO will implement all aspects of the U.N. resolution. Nothing more, nothing less," he said.
Amid complaints that he was not consulting enough with Congress, Mr. Obama held a teleconference on Friday with a bipartisan group of key members of Congress. During the call, Mr. Obama and other U.S. officials emphasized that the U.S. military role would be decreasing.
Polls have generally shown that most Americans support Mr. Obama's decision to order the air strikes. A key remaining issue is whether Libya's rebels can gain ground under the protection of Western air support.
Libyan state television reported Sunday that international air strikes were targeting Qaddafi's hometown and stronghold of Sirte for the first time.
Earlier Sunday, Qaddafi's regime lost further territory to rebels.