WASHINGTON - Libyan rebels have lost momentum and are not likely to dislodge Muammar Gaddafi from power, top US intelligence officials said on Thursday as Washington backed further away from any military action.

The White House said the United States would send civilian disaster relief teams to rebel-held eastern Libya to help with humanitarian efforts but stressed they would not be accompanied by military or security personnel.

As Washington, NATO and the United Nations search for the best way forward, Secretary of State Hillary Clinton said she would meet members of Libya's opposition groups but warned of "a situation whose consequences are unforeseeable" if the United States were to act on its own.

Critics of the Obama administration's stance on Libya are pushing for more forceful intervention, including direct military aid to outgunned rebel groups made up of enthusiastic but ill-trained civilians and dissident soldiers.

Obama has scheduled a news conference on Friday at 11:15 am EST (1615 GMT). The White House said he would address issues including rising energy prices. He is certain to face questions about the turmoil in Libya.

The top US spy official, noting Gaddafi's forces were better equipped and disciplined than the opposition, said eventually "the regime will prevail."

National Intelligence Director James Clapper's comments at a Senate hearing caught the White House off guard and led one Republican lawmaker to call for his dismissal for "undercutting" US efforts to remove Gaddafi.

President Barack Obama's national security adviser, Tom Donilon, criticized Clapper's analysis as "a static and one-dimensional assessment."

He said it placed too much emphasis on Gaddafi's military strength and did not take into account other factors, such as the international efforts to isolate him.

Clapper said without a decisive victory by either side, it was possible the North African oil-producing country could break into two or more semi-autonomous states, with Gaddafi retaining control of the capital, Tripoli, and its environs, and the rebels holding on to the eastern city of Benghazi.

Testifying at the same hearing, the head of US military intelligence, Lieutenant General Ronald Burgess, said Gaddafi "seems to have staying power, unless some other dynamic changes at this time."

NO CONSENSUS ON ACTION

As Clapper and Burgess delivered their assessments, NATO defense ministers meeting in Brussels shied away from direct military intervention while agreeing to move warships closer to Libya and continuing to plan for all options.

Despite the sense of caution, analysts say the United States and its allies may be forced to intervene if attacks by Gaddafi's forces result in heavy civilian casualties.

Recent successes appear to have emboldened Gaddafi, with his most prominent son telling Reuters that loyalists were preparing a full-scale offensive.

"It's time for action," Saif al-Islam Gaddafi said. "The Libyan people, we will never ever welcome NATO, we will never ever welcome Americans here. Libya is not a piece of cake."

Clapper's view that Gaddafi's forces had the upper hand and looked set to prevail led to renewed calls for Obama to take swift action to help the rebels.

"If the head of our intelligence community says, left alone, Gaddafi will not only not go but will defeat the opponents, then it seems to me to make it even more urgent to do something," said Senator Joe Lieberman, an independent.

Even though Lieberman, Democratic Senator John Kerry and Republican Senator John McCain are among those pressing for a "no-fly" zone over Libya and other military steps, there is no consensus on Capitol Hill about what to do.

If Gaddafi does survive and hold on to Tripoli, that could hurt Obama politically. The president would face accusations from Republicans that he allowed Gaddafi to stay in power and signaled to other rulers in the region that using force to crush dissent does not carry consequences.

US national security officials have told Reuters the Obama administration is deeply resistant to any military involvement in Libya, including arming the rebels.

It fears becoming entangled in a third Middle East war and giving al Qaeda a propaganda coup, the officials say.

Even sending the disaster relief teams is not without danger. Rebels briefly imprisoned a British diplomatic team last week, embarrassing London.

Clinton, who has said the UN Security Council must back any intervention in Libya, also echoed warnings by Defense Secretary Robert Gates about the limits of a no-fly zone.

"We had a no-fly zone over Iraq. It did not prevent Saddam Hussein from slaughtering people on the ground and it did not get him out of office," Clinton said.

Clapper said Gaddafi had about 80 operational aircraft -- a mix of helicopters, transport aircraft and fighter jets. The warplanes were struggling to "shoot straight" because they were relying on visual, rather than computer, targeting and had not caused very many casualties, he said.

The spy chief said Libya had the second-largest air defense system in the Middle East, with about 31 surface-to-air missile sites and a large number of portable surface-to-air missiles.