COMBAT OUTPOST SPERA, Afghanistan (AP) — U.S. troops were strapping on their gear for a 3:30 a.m. patrol along Afghanistan's border with Pakistan when word came to stand down: Soldiers were hearing heavy radio chatter among insurgents, raising suspicions of a coming attack.

Within 20 minutes the shooting had started, continuing steadily for two hours while militants attacked tiny Combat Outpost Spera from three sides with small arms and rocket-propelled grenades. Troops from the 101st Airborne Division fought back with rifles, heavy machine guns, and grenade launchers until the insurgents faded away at dawn.

The March 29 battle was typical of those at tiny bases known as combat outposts, or COPs, which are being re-evaluated as more emphasis is being placed on using forces to defend population centers.

Last week's withdrawal from the Korengal Valley, the scene of some of the war's most intense fighting, underscored the new policy, and was tacit admission that maintaining remote, difficult-to-defend outposts was not the best use of resources.

Still, the soldiers at COP Spera — where it will be maintained or abandoned isn't yet clear — believe the post is important in disrupting insurgent operations and cross-border infiltration in the eastern province of Khost.

"It's important for the local people, all my guys understand that," said 1st Sgt. Jason Scapanski of Foley, Minnesota. "Securing this area also secures the local people and if we can bring stability into this area we can start to work on the schools and the clinics that they're asking for."

Spera is a speck of a base, a collection of sandbags, tents and plywood buildings about half the size of a football field, surrounded by ramparts of mud brick, stone, and sand-filled barriers. A 20-minute helicopter flight from sprawling Forward Operating Base Salerno — one of the largest U.S. installations in eastern Afghanistan — the outpost is regularly manned by one U.S. platoon of 20-30 troops serving 10-week rotations along with an Afghan National Army company about 100-strong.

Thrown up soon after the arrival of U.S. forces in 2001, COP Spera commands a dry riverbed and rutted dirt road that lead into Pakistan and the commercial center of Miran Shah, a major insurgent base in northwestern Pakistan. Along with guarding the heights, troops here run daily patrols and help train Afghan forces in everything from maintaining their weapons to setting ambushes.

Insurgents have long valued the cross-border mountain gap as a route for moving men and material, and the chief operators in Khost now are believed to be the Haqqani network, an autonomous Afghan Taliban faction with close ties to al-Qaida.

Operating almost entirely under cover of night, insurgents launch an average of two to three attacks a week against Spera, mainly with rockets and small-arms fire and mostly to little effect. Since the beginning of the year, Spera has suffered just one casualty, a soldier injured by shrapnel from a rocket-propelled grenade. He is expected to return to duty soon.

COP Spera, along with units based in the more densely populated Afghan interior, frustrates the Haqqani's attempts to isolate Khost from the surrounding region and extend their reach to the capital Kabul and the country's volatile south, said Col. Viet Luong, overall commander of U.S. forces in Khost and the border provinces of Paktiya and Paktika.

"You have to be able to disrupt enemy fighters from coming in and putting pressure on the population," Luong said at his office at FOB Salerno.

The border with Pakistan is simply too long and porous to be policed in its entirety, so the next best strategy is containment, Luong says. And while redeployments are being considered, any U.S. troops withdrawn would be replaced by Afghan Border Police units whose commanders are being mentored by American officers, he said.

"It's key terrain, so you can't just displace from that and allow the enemy the freedom of movement," Luong said.

While plans to move troops away from remote outposts have long been in the works, they were hastened by an attack in October on COP Keating north of Khost that left eight American soldiers dead. A year before, nine Americans were killed at an outpost near Wanat.

Both posts were given up, and insurgents trumpeted the U.S. pullbacks as defeat, with their fighters shown in videos swarming through the abandoned bases.

Command Sgt. Maj. Michael T. Hall, the top enlisted man among international troops in Afghanistan, says that's to be expected but won't affect the goal of deploying limited resources in the most effective way.

"We don't and never will have enough troops to control the entire country," Hall said. "We have limited resources and we have to decide where best to place them."

Away from questions over strategic value, outposts provide some other benefits, particularly in boosting Afghan security capabilities — the linchpin of the Pentagon's strategy to transfer responsibility to Afghan forces so U.S. troops can go home.

"We're very clear on our mission and we've gotten the message around to the Taliban that we're here we're not leaving," said Pfc. Cameron Thornton of Sacramento, Calif.