By BRADLEY KLAPPER
WASHINGTON - President Barack Obama insisted Thursday that Libyan leader Moammar Gadhafi "step down from power and leave," his most explicit statement of support for rebels challenging Gadhafi's four-decade rule in a region convulsed by uprisings against authoritarian regimes. Gadhafi has vowed to stay.
Obama did not rule out establishing a "no-fly" zone over Libya, a move that his Pentagon chief said a day earlier would amount to an act of war because it would require bombing Libya's air defenses. Although Obama said he was considering a full range of options, he emphasized the U.S. role in helping refugees and heading off a humanitarian crisis.
"Let me just be very unambiguous about this. Col. Gadhafi needs to step down from power and leave," Obama said at a White House news conference with Mexican President Felipe Calderon.
Obama announced that U.S. military aircraft would play a humanitarian role by helping Egyptians who had fled the chaos in Libya and become stranded in Tunisia. The planes are to fly them from Tunisia back to Egypt. The Pentagon has ordered two Navy warships into the Mediterranean, but Obama did not discuss the possibility of specific military actions such as providing air cover for rebels.
U.S. aircraft could leave as early as Friday for the first mission to help Egyptians in Tunisia return home, senior defense officials said. The officials spoke on condition of anonymity because plans have not been officially announced.
Obama offered his most extensive remarks on the Libya crisis on a day when rebels strengthened their hold on the strategic oil installation at Brega after repelling an attempt by Gadhafi loyalists to retake it. Obama said his main focus was on limiting civilian deaths, while acknowledging his fear that the crisis could devolve into deadlock.
" There is a danger of a stalemate that over time could be bloody," he said. "That is something that we are obviously considering." He raised the possibility of Gadhafi hunkering down in the capital of Tripoli while his people suffer food shortages. Obama said the U.S. and its partners would have to consider how to get food in.
Obama also appeared to suggest that Gadhafi loyalists switch sides in support of the revolutionaries.
"Those around him have to understand that violence that they perpetrate against innocent civilians will be monitored and they will be held accountable for it," Obama said. "And so to the extent that they are making calculations in their own minds about which way history is moving, they should know history is moving against Col. Gadhafi."
The U.S. administration has been tempering tough talk on Libya with a dose of reality, explaining that even a no-fly zone to control the skies over the country would require a military attack. Two leading senators on defense matters responded Thursday by urging a strong U.S. stance aiding Gadhafi's opposition.
The Pentagon is making it clear it doesn't want war.
A statement Wednesday by Defense Secretary Robert Gates illustrated the administration's effort to rein in "loose talk" about military options to force Gadhafi from power. It was an acknowledgement that, short of an unlikely military offensive by a U.S.-led coalition, the options for international action to stem the violence are highly limited.
"Let's just call a spade a spade: A no-fly zone begins with an attack on Libya to destroy the air defenses," Gates told a congressional panel. The Pentagon could get the job done if ordered by the president, he said, but he noted that an attack would require more air power than a single U.S. aircraft carrier, which typically carries about 75 planes. "It is a big operation in a big country," Gates said.
On Thursday, Sen. John McCain, R-Ariz., took issue with Gates' comment about "loose talk," saying he believed it was well within the U.S. military's capabilities to shoot down Libyan aircraft.
"May I just say, personally I don't think it's 'loose talk' on the part of the people on the ground in Libya or the Arab League or others, including the prime minister of England, that this option should be given the strongest consideration," McCain said.
Endorsing McCain's remarks, Sen. Joe Lieberman, I-Conn., said another option was to provide U.S. air defense weapons to the Libyan rebels and to train them in their use.
The unspoken subtext to Gates' remarks on Wednesday was that with U.S. forces already deeply committed in Afghanistan, still winding down military operations in Iraq and on the watch for surprises in Iran and elsewhere in the volatile Persian Gulf region, the risks associated with military action in Libya might be unacceptable.
Secretary of State Hillary Rodham Clinton said Wednesday that the crisis calls for a mix of diplomacy and defense.
"We are taking no option off the table so long as the Libyan government continues to turn its guns on its own people," Clinton said. But she told two separate Senate subcommittees that the U.S. government was far from being in a position to commit to a military response, even as she outlined grave concern about the instability affecting the North African country.
Some U.S. allies in NATO are mulling the idea of creating a no-fly zone over Libya. But Germany cautioned Wednesday against playing into charges that the West is unduly meddling in Arab affairs.
Associated Press writers Matthew Lee, Robert Burns, Donna Cassata and Pauline Jelinek in Washington and Gregory Katz in London contributed to this report.