WASHINGTON - (AP) - Defending the first war launched on his watch,President Barack Obama declared Monday night that the United Statesintervened in Libya to prevent a slaughter of civilians that wouldhave stained the world's conscience and "been a betrayal of who weare." Yet he ruled out targeting Libyan leader Moammar Gadhafi,warning that trying to oust him militarily would be a costlymistake. Obama announced that NATO would take command over the entireLibya operation on Wednesday, keeping his pledge to get the U.S.out of the lead but offering no estimate on when the conflict mightend. He never described the U.S.-led military campaign as a "war"and gave no details on its costs, but he offered an expansive casefor why he believed it was in the national interest of the UnitedStates and its allies to act. In blunt terms, Obama said the military intervention had stoppedGadhafi's advances and halted a slaughter that could have shakenthe stability of an entire region. "To brush aside America's responsibility as a leader and - moreprofoundly - our responsibilities to our fellow human beings undersuch circumstances would have been a betrayal of who we are,"Obama said. "Some nations may be able to turn a blind eye toatrocities in other countries. The United States of America isdifferent. And as president, I refused to wait for the images ofslaughter and mass graves before taking action."