The last of the American soldiers packed up their gear, lowered their flag and flew away on Chinook helicopters Thursday, handing this small base to the 250 Afghan policemen left in the swirling dust below.

Just 25 miles from the Pakistani border, in one of Afghanistan’s most volatile provinces, the hand-over marked the beginning of an experiment to see whether Afghan security forces are ready to fight the Taliban as U.S. troops begin to withdraw.

“Is there a risk it could all fall apart? Probably a small risk,” said Col. Edward T. Bohnemann, the brigade commander in Paktika, where the base is located. “I look at it, honestly, as a huge win, saying, ‘Hey, we’ve demonstrated the Afghan security forces are capable of taking this.’ ”

The decision to leave Waza Khwah — the largest base yet to be handed over to Afghan forces — represents the type of calculation that will become more common, and more difficult, as 33,000 U.S. troops begin to withdraw later this year amid a resilient Taliban insurgency. American commanders have accelerated the plan to transfer security responsibility to Afghan troops between now and 2014.

The Afghan battalion’s performance in the coming months will be watched closely, and more such hand-overs are likely, Bohnemann said. “I think it’s going to be replicated, duplicated across [eastern Afghanistan] at a much faster rate than people expected,” he said.

Taliban action expected

Southern Paktika is the calmest part of the province. But even here, U.S. officers expect that with the Americans gone, the Taliban will try to test the Afghan border police battalion by attacking with greater intensity. They also said the Taliban might attempt to divert more fighters from Pakistan up through this southern entry into the province to avoid the more hotly contested eastern border.

“I do think they’ll try to prod and poke at Waza Khwah,” Maj. Eric Butler, the brigade’s intelligence officer, said of the Taliban. “I don’t think there’s going to be a massive attack.”

The American soldiers who work with this battalion say they believe it can handle the threat. The officers in the Afghan border police unit have shown “they now outmatch the insurgency by a significant-enough margin that we can change our relationship,” said Lt. Col. Curtis D. Taylor, the battalion commander in this part of Paktika province.

That unit, the 7th battalion of the Afghan border police, is considered one of the best in the province. Over the past couple of years, the unit’s American partners have dwindled from a several-hundred-strong battalion down to an artillery battery of about 80 soldiers who have rarely fired a shot in the four months they’ve been deployed at Waza Khwah. Those soldiers are moving to a base farther north in the province, where Taliban and Haqqani network fighters pose more-lethal problems.

The 7th battalion has gathered intelligence and conducted its own operations independent of U.S. troops. It is patrolling more often, with more men, and has come under fire about once a week, said Lt. Col. Chris Niesen, the lead American adviser with the border police at Waza Khwah.

“You are safe to about a 15-kilometer radius. After that it gets fun,” Niesen said. But the “security situation has been maintained mostly, in the last three months, by the Afghans.”

“They’re doing it all by themselves,” he said.

Afghan officials were generally optimistic about the prospects that border police could secure the area. The provincial governor, Mohibullah Samim, called the hand-over a “big steppingstone” in the war and said, “We are not worried about any problems, because we’re sure the police will be able to take care of themselves.”

One of the regional police officers, Col. Zahir Gul, said taking over the base brought a “great deal of responsibility.” He told the police officers assembled for the ceremony, “I want you to be very careful with this.”

Tricky logistics

Decisions about where to transfer U.S. and NATO responsibility to Afghan security forces are taking place all over the country. The first seven areas for such transition were chosen this year, and President Hamid Karzai’s government is finalizing a second batch.

The first areas to be transferred were some of the country’s safest. But as the process accelerates, coalition and Afghan commanders will face more-difficult choices about giving Afghan security forces the lead role in violent terrain. So far, the transition has rarely involved American troops pulling out of a base entirely, though that will become more common.

The trickiest aspects of such hand-overs are often less about fighting than about mundane logistical matters. The border police at Waza Khwah cannot call in their own medevac helicopters or supplies by air the way the U.S. unit could. The urgency of a hand-over deadline has forced the battalion to confront issues such as paying salaries and repairing vehicles and generators.

Without that deadline, “I think they would have more or less stagnated with some level of dependency on U.S. forces,” Taylor said. “That propelled the growth for the unit forward.”

American soldiers will keep a locked compound on the base, known as the Alamo, that they will visit periodically to advise the battalion. They plan to fly Apache attack helicopters overhead as an occasional show of force and deliver some supplies as needed. Taylor said U.S. medevac helicopters will be available to the border police at their request.

“We’re not cutting ties completely,” he said.

Afghan border police officers were undaunted by the task ahead.

“We will destroy the enemy,” said Capt. Khalil Ahmadi, commander of the 7th battalion. “We will control the border.”