By Caren Bohan and Phil Stewart
WASHINGTON (Reuters) - President Barack Obama and British Prime Minister David Cameron agreed on Tuesday that Libyan leader Muammar Gaddafi must leave power quickly and weighed steps to stop the bloodshed, including a no-fly zone.
As Obama faces growing calls at home to help Libyan rebels seeking Gaddafi's ouster, he and Cameron discussed a "full spectrum of possible responses" during their telephone call, the White House said in a statement.
The two leaders would work on planning for several options, including surveillance of Libya with spy planes, humanitarian assistance, enforcement of a United Nations arms embargo and a no-fly zone, it said.
"They agreed that the common objective in Libya must be an immediate end to brutality and violence; the departure of Gaddafi from power as quickly as possible; and a transition that meets the Libyan peoples' aspirations for freedom," the White House said.
As the international community tries to reach consensus on what to do about Libya, Britain and France are working on a U.N. Security Council resolution for a no-fly zone that could be put forward if they believe conditions warrant it.
British Foreign Secretary William Hague said on Tuesday a no-fly zone was a practical possibility but would require "a clear legal basis, a demonstrable need and strong international support and broad support in the region and a readiness to participate in it."
Cameron told the BBC that planning was needed in case Gaddafi refuses to step down.
"I think now we have got to prepare for what we might have to do if he goes on brutalizing his own people," he said.
LITTLE EFFECT ON HELICOPTERS
Obama is facing criticism, especially from Republicans, that he has been too cautious during the turmoil in Libya.
But the Obama administration is reluctant to get drawn into the conflict while the United States is entangled in Iraq and Afghanistan, stressing the need for international backing for any foreign military intervention.
U.S. officials have voiced concerns about the effectiveness of a no-fly zone.
Marine General James Amos told U.S. lawmakers that Libya's helicopter forces represent its strongest air power threat.
"There are several things that will give (Gaddafi's forces) enormous advantage. One is the ground movement of forces, vehicles," Amos said. "I think it's more than just aviation. I think it's very complex."
Senator John McCain, a vocal proponent of a no-fly zone, said he could not understand why Obama was resisting growing pressure to impose one.
"People are dying. The facts are very clear," McCain told Reuters as he left the hearing where Amos testified. "President Obama has said that Gaddafi has got to go. Wouldn't a no-fly zone be a very important way to make that happen?"
Senator John Kerry, a close Obama ally, has called for the United States to prepare for a no-fly zone and has floated the idea of bombing Libyan runways to ground Gaddafi's warplanes.
(Additional reporting by Susan Cornwell, Alister Bull and Arshad Mohammed; Writing by Caren Bohan; Editing by John O'Callaghan and Eric Walsh)