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.”

At the same time, he said, “a range of options are on the table at NATO.”

NATO defense ministers, meeting in Brussels, authorized the repositioning of allied warships closer to Libya to strengthen surveillance of the fighting there and to better monitor a U.N. arms embargo against Gaddafi’s forces. Defense Secretary Robert M. Gates made it clear, however, that the NATO ships would not be authorized to take any military action without a new U.N. Security Council resolution.

Gates said NATO planners will continue to look into what would be necessary to impose a no-fly zone on Gaddafi’s air force. But he indicated that no more specific preparations were underway.

“That’s the extent of it as far as a no-fly zone is concerned,” Gates told reporters.

The limited NATO actions added to an impression that members of the U.S.-led alliance, at least for the moment, seek to threaten Gaddafi with gestures while holding back from more concrete measures until they can muster legal authority. The United States and its European allies think the case for military action would be strengthened at the United Nations if the Arab League agrees to back intervention when it meets Saturday to discuss Libya.

Libyan “bombing attacks that the world could see and understand, and it could be verified, on civilian and populated areas . . . would massively strengthen the case for the introduction of a no-fly zone,” British Foreign Secretary William Hague told the BBC.

“Of course, it may involve many other nations, if it happens, other than NATO,” he said. But “the demand is mounting in the Arab world. That is very important, it’s absolutely crucial, in bringing a no-fly zone into being.”

Donilon said that any military action would require “not just rhetorical support” from the region. A European official said that no one expected Arab nations to send aircraft to patrol Libya but that it would help if some Arab governments would provide token support by, for example, sending senior military officials to participate in a command-and -control facility.

The case made by U.S. lawmakers who favor more immediate aggressive action appeared to be bolstered by testimony from Clapper, the director of national intelligence, who told the Senate Armed Services Committee that Gaddafi was likely to “prevail” over the rebels without foreign intervention or some other major change.

“I think, frankly, they’re in for a tough row,” Clapper said of the opposition in response to a question from Sen. Joseph I. Lieberman (I-Conn.). “I do believe that Gaddafi is in this for the long haul. I don’t think he has any intention . . . of leaving.”

Donilon, when asked whether Clapper’s assessment diverged from that of the White House, said the intelligence chief had offered a “static” assessment of the weaponry and forces arrayed on both sides, without taking into account the “dynamic” of Gaddafi’s international isolation and other pressures being brought to bear against him.

“I’m one of those who believes that absent international authorization, the United States acting alone would be stepping into a situation whose consequences are unforeseeable,” Clinton said in testimony before a House appropriations subcommittee. “And I know that’s the way our military feels.”

“It’s easy for people to say do this, do that, and then they turn and say, okay, U.S., go do it. You use your assets. You use, you know, your men and women; you go out and do it and then you take the consequences if something bad happens,” she said.

Clinton said she would meet with Libyan opposition figures when she travels next week to Tunisia and Egypt as the most senior administration figure to visit those countries since their entrenched governments were ousted earlier this year by largely peaceful protests.

“We are attempting and working overtime to figure out who are the people that are now claiming to be the opposition,” she said, “because we know that there are some with whom we want to be allied and others with whom we would not.”

The State Department declined to specify with whom Clinton would meet, but Donilon said they would be the same Libyan opposition figures currently traveling in Europe: council representatives Mahmoud Jibril and Ali al-Essawi.

French President Nicolas Sarkozy met with them Thursday at the Elysee Palace, a measure depicted as a gesture of support for the rebellion. French officials said they would soon send an ambassador to Benghazi, the center of the anti-Gaddafi movement, to establish regular contact with the rebel organization. Essawi said the council planned to send a representative to Europe.

Preceding a meeting of the 27 European Union heads of state Friday, Sarkozy and British Prime Minister David Cameron sent a letter calling on the bloc to “send the clear political signal that we consider the Council to be valid political interlocutors, and an important voice for the Libyan people in this phase.”

Cody reported from Brussels. Staff writer Craig Whitlock contributed to this report.