Obama 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.
Obama asserted in his weekly address on Saturday that the U.S. mission was "clear and focused," is succeeding, has taken out Gadhafi's air defenses and has saved "the lives of countless citizens" who were threatened by Gadhafi.
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.