Obama defended his decision to join a military coalition that is enforcing a United Nations no-fly zone over Libya, saying the U.S. had to intervene to prevent a slaughter of civilians.
However, he ruled out targeting Moammar Gadhafi, warning that trying to oust him militarily would be a costly mistake.
Obama said, "History is not on Gadhafi's side," and that, "The Libyan people will be able to determine their own destiny."
The president said that NATO would take command over the entire Libya operation on Wednesday, keeping his word to get the U.S. out of the lead.
Obama offered his case for why he believed it was in the national interest of the U.S. and allies to act.
He said the U.S.-led response had stopped Gadhafi's advances and halted a slaughter he warned could have shaken the stability of an entire region. He also said it could be more costly for American tax payers had the U.S. not taken immediate action.
The president's speech came as rebels seized more cities.
Rebels told Al Jazeera on Monday that they've captured Moammar Gadhafi's hometown, but the news organization hasn't been able to independently verify that report.
Gadhafi's hometown of Sirte is located about halfway between the rebel-controlled east and the Gadhafi held capitol of Tripoli. Libyan state TV reported air raids in both Sirte and Tripoli.
What is clear is that the rebels are making significant progress. The rebels said they captured more than 300 miles of territory. Included in their conquests are key oil facilities. Because of that, the price of crude oil dropped slightly Monday to below $105 a barrel.
NATO approved a plan over the weekend to take over the leadership role from the U.S. The allies will control all aerial operations and ground attacks.
"We are already enforcing the arms embargo and the no-fly zone, and with today's decision we are going beyond," said NATO secretary general Anders Fogh Rasmussen. "We will be acting in close coordination with our international and regional partners to protect the people of Libya."
Russia criticized the campaign, saying it had overstepped its U.S. mandate to protect civilians and had taken sides in a civil war. NATO's commander had a different take.
"Our goal is to help protect civilians and population centers from attack or that are under threat of being attacked in Libya," said Lt. Gen. Charles Bouchard.
NATO has made clear their goal is not to remove Gadhafi from power. Obama, on the other hand, has said he wants Gadhafi to go. But Defense Secretary Robert Gates told ABC News the U.S. military won't force that to happen.
"I think you don't want ever to set a set of goals or a mission, military mission, where you can't be confident of accomplishing your objectives. And as we have seen in the past, regime change is a very complicated business," Gates said. "It sometimes takes a long time. Sometimes it can happen very fast, but it was never part of the military mission."
Gates also said Libya does not pose an imminent threat to the U.S.
Critics in Congress said the president hasn't made his strategy clear to them so far. The White House said during Obama's address, he will lay out the U.S. policy for Libya going forward.
In an Eyewitness News poll, respondents were asked, if airstrikes don't force Gadhafi out, would they support sending in U.S. ground troops.
Seventy percent said they opposed the move, 20 said they would support it and 10 percent answered that they were not sure.
The Associated Press contributed to this report.