Up to 1,000 fighters loyal to Usama bin Laden either fled or were seized on Saturday, while others were overheard debating surrender over two-way radios.

Aided by U.S. special forces in the White Mountains of eastern Afghanistan's Tora Bora region, relentless attacks collaborated by American warplanes and tribal forces of the eastern alliance seem to be paying off as this last group of Al Qaeda resistance crumbles.

Defense Secretary Donald H. Rumsfeld, told reporters on his way to Central Asia that a group of 50 Al Qaeda fighters had surrendered, and that those that remained were quickly running out of ways to escape.

One fighter said 60 Chechens had fled, deserting six of their wounded and many dead. He asked his commander, Hazrat Ali on radio frequencies of the eastern alliance, "What do you want us to do with them?" Ali said they should be held while he sent in back-up.

Mohammed Khan, the front-line commander, said three captured Arabs told him 50 Al Qaeda leaders fled on mules early Saturday toward the Pakistani border, only a few miles away. "They are commanders, but not the top commanders. They are escaping one by one or two by two," he said. It was not clear whether they were the same fighters Rumsfeld mentioned.

In an effort to stop others from fleeing, Pakistan has sent troops and helicopters to guard the border.

Other fighters argued in Arabic over their radio frequencies about whether they should surrender. Khan said a group of Arabs wanted to surrender, but another group of Chechen fighters were trying to persuade them not to. Two emissaries approached the front line to announce 300 men wanted to give up, but the men never emerged, said fighter Said Mohammed Pawhalan.

The eastern alliance — wary after two surrender deals fell apart this week — pressed their assault.

"Don't give them time! They're taking advantage of time," an eastern alliance commander said over the radio.

Gen. Tommy Franks, the U.S. commander of the war, said he would not know until at least Saturday how many Al Qaeda prisoners had been taken or whether any were senior leaders of bin Laden's terrorist network. He said they would be screened by U.S. forces.

U.S. airstrikes continued around the area, including on mountain ridges where bombs had not previously fallen. That could indicate the Americans were attacking fleeing fighters.

Eastern alliance forces battled close to the mouth of a cave which hundreds of Al Qaeda fighters were defending, and which Ali said was bin Laden's personal cave. Radio traffic indicated machine-gun fire was coming from the mouth of the cave, and B-52 bombers and fighter jets continued to pound the area.

"I don't know, but I think there is a place inside where Usama is," Ali said.

Twelve U.S. special forces fighting with the Afghans came under heavy fire from a machine-gun nest Friday, said Khawri, an Afghan fighting with them. Two Americans were grazed by bullets, but were well enough to walk down the mountain. Franks had no information on Americans being wounded but could not rule it out.

In southern Afghanistan, U.S. Marines were expected to transfer the bulk of their forces from Camp Rhino, a desert airstrip, to Kandahar's international airport, which they seized Friday in their largest mobilization in Afghanistan.

Hundreds of Marines were checking for mines and booby traps in the terminal building, and a commander declared the runway fit for aircraft. The airport is to become a major arrival point for humanitarian aid that will be desperately needed as winter settles on Afghanistan.

Franks called the battle around Tora Bora "pitched" and estimated the number of Al Qaeda fighters at 300 to 1,000.

In addition to those near the cave, up to 600 others were believed to be cornered in an 8-square-mile forest nearby, just miles from the Pakistan border.

A large bomb fell on the forest Friday evening, sending up a huge and lingering fireball that was visible two miles away. U.S. bombers and AC-130 Spectre gunships circled over the ridge where the suspect cave was located, pounding defensive positions.

Pakistan's army set up 300 checkpoints along the border to prevent fleeing Al Qaeda fighters, officials said in the Pakistani capital, Islamabad.

"We have made it impossible for bin Laden to enter our country," said Pakistan's interior minister, Moinuddin Haider.

Pakistan has enhanced ground and aerial surveillance, including helicopter gunships. Troops on horses and mules have been seen moving to centuries-old caves to tighten the noose on fleeing fighters.

A $25 million bounty for bin Laden — prime suspect in the Sept. 11 terror attacks on the United States — has whetted the appetite for finding him.

While bin Laden was the focus of the fierce conflict at Tora Bora, some officials say he is more likely holed up in another part of Afghanistan, nearer Kandahar in the south, or even may have left the country.

The Associated Press contributed to this report.