The top U.S. intelligence official said Thursday that Libyan leader Moammar Gaddafi is likely to "prevail" in his battle against rebels without foreign intervention or some other major change, as European governments and U.S. lawmakers sought ways to aid Gaddafi's increasingly beleaguered opponents.

The prediction by James R. Clapper, the director of national intelligence, came as the Gaddafi government claimed it has regained control of Zawiyah, an oil-refining center 27 miles west of Tripoli, and has driven rebels from the key oil port of Ras Lanuf in the east.

Clapper told a hearing of the Senate Armed Services Committee that Gaddafi has consolidated his position in recent days and that his forces are far better equipped than the rebels, giving him a clear advantage.

"With respect to the rebels in Libya and whether or not they will succeed . . . I think, frankly, they're in for a tough row," Clapper said. "I do believe that Gaddafi is in this for the long haul. I don't think he has any intention . . . of leaving."

In response to questions, he added that "from a standpoint of attrition" and given the government's greater resources, "I think [over] the longer term that the regime will prevail."

President Obama's national security adviser, Thomas E. Donilon, later told reporters that the United States would soon send civilian disaster relief teams to eastern Libya to provide humanitarian aid.

"These are humanitarian assistance teams," Donilon said. "They are not going in any way, shape or form as military operations." The teams from the U.S. Agency for International Development will operate "with the cooperation of the authorities" in rebel-controlled areas, Donilon said.

In Tripoli, Gaddafi's son, Saif al-Islam Gaddafi, vowed to about 2,000 frenzied supporters that the Libyan army would press ahead with its offensive and march on Benghazi, the rebel capital 630 miles to the east.

"Hear it now, I have only two words for our brothers and sisters in the east: we're coming," he roared at the crowd, pumping his fist. "Tonight Ajdabiya, tomorrow Benghazi," the crowd roared back. Ajdabiya is about 100 miles south of Benghazi, the rebel stronghold that is Libya's second-largest city.

Libya's deputy foreign minister, Khaled Kaim, told reporters that the Libyan military had managed to "clean" Ras Lanuf completely and had recaptured weapons seized by the rebels.

He also said that Libyan forces recaptured Zawiyah and were now "cleaning" the town in preparation for a visit by journalists to verify the claim.

In the Armed Services Committee hearing, Army Lt. Gen. Ronald L. Burgess Jr., director of the Defense Intelligence Agency, agreed with Clapper that Gaddafi was not at immediate risk of being toppled. "Right now he seems to have staying power, unless some other dynamic changes at this time," he said.