Gates told a Pentagon news conference that the Predator is an example of the unique U.S. military capabilities that Obama is willing to contribute to a coalition military campaign in Libya, while other countries enforce a no-fly zone.
Marine Gen. James Cartwright, speaking alongside Gates, said the first Predator mission was scheduled for Thursday but it was scratched due to poor weather. Cartwright said the Predators allow low-level precision attacks on Libyan government forces.
Libyan rebels said Thursday they had control of a post on the Tunisian border, forcing government soldiers to flee over the frontier and possibly opening a new channel for opposition forces in Muammar al-Qaddafi's bastion in western Libya.
In the rebel stronghold of Benghazi in eastern Libya, meanwhile, relief workers and medical teams awaited the arrival of a passenger ferry carrying about 1,000 people -- mostly Libyan civilians and workers from Asia and Africa -- out of the besieged city of Misrata, the main rebel holdout in Qaddafi's territory.
Also aboard the vessel were the bodies of an Oscar-nominated documentary maker from Britain and an American photographer who were killed covering clashes Wednesday. A day earlier, the ferry arrived in Misrata, delivering food and medical supplies to the beleaguered population.
Rebels appear to be gaining more international support, including plans by Italy, France and Britain to send combat advisers and other nations pledging communications and other equipment under the NATO mission. But Qaddafi's regime fired back with fierce threats if the alliance sends any troops to Libya.
"If NATO comes to Misrata, or any Libyan city, we will unleash hell upon NATO," government spokesman Moussa Ibrahim told reporters in the capital Tripoli. "We will be a ball of fire. Libya will become one man, one woman, fighting for freedom. We will make it 10 times as bad as Iraq."
The reported capture of the border crossing followed three days of intense fighting outside the desert town of Nalut, about 140 miles southwest of the capital Tripoli, said a rebel leader, Shaban Abu Sitta. The area was briefly in hands of anti-government forces last month before Libyan troops moved in.
Holding the Dhuheiba border crossing could open important supply routes for anti-Gadhafi forces and give the rebels another foothold in western Libya.
"Rebels are now manning Dhuheiba crossing," said Abu Sitta, who claimed his fighters destroyed 30 army pickup trucks and captured 10 cars and some weapons.
Tunisia's official TAP news agency said Libyan rebels had control of the post and at least 13 Libyan military officers, including two commanders, fled across the border. The report, citing a "high-level" Tunisian military official, said the Libyan officers were detained and the border post was closed.
A doctor with Tunisia's Red Crescent, Dr. Mongi Slim, said the border post was in rebel hands and relief officials fear it could lead to a new wave of refugees.
"The main worry now is an influx of families fleeing the fighting" in Libya, Slim told The Associated Press. "Before, when the post was under the control of the pro-Qaddafi forces, people had been crossing on little paths. But now it will be much easier."
On the Ionian Spirit ferry -- part of a maritime lifeline to Misrata -- Libyan civilians and migrants workers packed the decks, hallways and every other available space. In the ship's Panorama Bar, evacuees tossed mattresses onto the wooden dance floor. Women slipped behind a curtain to change.
The injured were brought to the lower level of the ship, where an 11-member medical team set up a makeshift intensive care unit.
Jeremy Haslam, a coordinator from the Geneva-based International Organization for Migration, said the boat has more than 1,000 evacuees including 239 Libyan civilians and 586 migrants from Niger and others from Africa and Asia.
He said some Libyans tried to flee Misrata aboard a tug boat, but were turned away because the vessel was overcrowded. Some managed to get aboard the ferry.
"We are carrying more than we are supposed to but it's better than letting these people leave on a tugboat," said Haslam.
The number of people seeking to flee Misrata has surged as Libyan forces expand their shelling to areas once considered relatively safe havens from attacks. The government spokesman Ibrahim claimed Qaddafi forces control more than 80 percent of the city and the rebels hold "the seaport and the area surrounding it."
"Our neighborhood became a war zone so we had to get out," said Faiza Stayta, who made it aboard the ferry with her husband and two children. "All the firing is random. You hear a rocket and how have no idea if it will come down on your house."
The vessel carried the bodies of Chris Hondros, a New York-based photographer for Getty Images, and British-born Tim Hetherington, co-director of the 2010 Afghanistan war documentary "Restrepo" that was nominated for an Academy Award. The film was co-directed by Sebastian Junger, author of "The Perfect Storm."
They were killed Wednesday in an attack that also injured two other photographers. A statement from Hetherington's family said he was killed by a rocket-propelled grenade. The ship also held the body of a Ukrainian doctor killed Wednesday from an artillery blast, said Haslam of the IOM.
U.N. Secretary-General Ban Ki-moon, during a visit to the Ukrainian capital Kiev, said the doctor's wife was severely wounded by the shell.
He expressed his "deepest condolences for that couple. This is not just a couple, this is what Ukrainian people are showing to humanity to the world."
The group is planning to send another ship to Misrata carrying 500 tons of food and medical supplies. The IOM said it has evacuated more than 3,100 people from Misrata.