President Obama expressed concern Friday about a U.S. intelligence assessment that Moammar Gaddafi may have the firepower to win a war of attrition against Libyan rebels, but he insisted that "we are slowly tightening the noose" on the longtime leader.

Speaking to reporters at the White House a day after his director of national intelligence said Gaddafi was likely to "prevail" in a protracted conflict, Obama said the comment by James R. Clapper Jr. in Senate testimony was "a hard-headed assessment about military capability" and not a statement of policy.

Stating what he said was U.S. policy on Libya as determined by him, Obama added: "I believe that Gaddafi is on the wrong side of history. I believe that the Libyan people are anxious for freedom and the removal of somebody who has suppressed them for decades now. And we are going to be in contact with the opposition, as well as in consultation with the international community, to try to achieve the goal of Mr. Gaddafi being removed from power."

Obama said NATO members are meeting Tuesday "to consider a no-fly zone" over Libya that would ground Gaddafi's air force. "And we've been in discussions with both Arab countries as well as African countries to gauge their support for such an action," he said.

He said the United States is maintaining 24-hour surveillance of Libya to " have some sort of alert system if you start seeing defenseless civilians who are being massacred by Gaddafi's forces." He declined to specify what actions might be taken in that event but said he believes the United States and the international community have an obligation to do what they can to prevent the sort of slaughter that occurred in the Balkans and Rwanda in the 1990s.

On Thursday, the White House announced that it would send a government aid team into rebel-held parts of Libya, and Secretary of State Hillary Rodham Clinton said she would meet next week with rebel representatives in Cairo, moves that edged the Obama administration closer to the Libyan opposition.

But the administration stopped far short of recognizing the rebels' Transitional National Council as Libya's legitimate government and continued to wrestle with how to achieve its goals of pushing Gaddafi from power while ensuring that something better far replaces him.

The White House rejected criticism from some lawmakers that its response has been too slow to fast-moving events on the ground. On Thursday, Gaddafi loyalists routed opposition fighters from Ras Lanuf, a strategic oil port the rebels had held for a week, and said they had retaken the town of Zawiyah, 27 miles west of Tripoli.

Gaddafi's son, Saif al-Islam Gaddafi, triumphantly proclaimed to a crowd in the capital that forces loyal to his father would continue to reverse the rebels' gains. "Hear it now. I have only two words for our brothers and sisters in the east: We're coming," he said.

Thomas E. Donilon, President Obama's national security adviser, told reporters in a briefing that the United States and its partners had "taken a range of steps . . . to squeeze Gaddafi, isolate him, really turn him into a pariah."

"So I think it really is important in any analysis or writing that's done on this that those steps not be underestimated," Donilon said, adding that "half of the population of Libya is no longer under regime control." Although U.S. relief teams have been working along Libya's border in Tunisia and Egypt, he said, "we're prepared to send diplomats to Benghazi to engage the opposition inside Libya."

"This will be helpful to our understanding of the situation on the ground," Donilon said, and will "allow us to facilitate humanitarian assistance."