After weeks of hesitation and divisions among his advisers, President Barack Obama endorsed military action against Libya's Moammar Gadhafi, saying U.S. values and credibility are at stake to stop "the potential for mass murder" of innocents.

The U.S. military, which is already stretched thin by two wars and an expanding effort to assist disaster victims in Japan, would take a supporting role, Obama said, with European and Arab partners in the lead. He explicitly ruled out sending American ground forces into the North African nation.

A wide range of U.S. firepower stood ready, including Navy ships and submarines capable of launching Tomahawk cruise missiles with high-explosive warheads that could destroy air defense sites and other potential targets in the earliest stages of any allied military action.

In solemn remarks at the White House, Obama never used the word "war," but that is what U.S. forces could face if Gadhafi refuses to comply with United Nations demands. It is widely anticipated that a first step in imposing a no-fly zone over Libya - a tactic aimed at keeping Gadhafi's planes from attacking - would be assaults on the country's coastal air defenses, The Associated Press reported.