KANDAHAR, Afghanistan – When the U.S. and Afghan militaries launch their long-awaited Kandahar operation as early as this weekend, the key to its success may lie in some obscure mountain roads that connect the dusty heartland of the Taliban insurgency with a fertile valley nearby.

One is the “Ant Pass,” a rocky, windswept passage through which Taliban fighters shuttled in and out of Kandahar, Afghanistan’s second-largest city, to attack U.S. convoys, assassinate Afghan government officials, plant roadside bombs and target international development offices.

After a series of frustrating delays, American and Afghan forces aim to transform this narrow gateway into a crucial choke point on the eve of the initial showdown in the fertile Arghandab Valley, which stretches out below the pass.

With U.S. soldiers keeping watch, specially trained Afghan police officers stand alongside towering new concrete barriers that divide the two-lane highway that runs from the Arghandab into one of Kandahar’s more Taliban-friendly neighborhoods.

In the coming days, hundreds of Afghan fighters and American soldiers will descend on the Arghandab in an attempt to push an estimated 150 to 200 Taliban militants out of the valley’s network of vineyards and pomegranate groves.

The long-anticipated battle, a campaign that is expected to last about two weeks, will be the first serious test for U.S. and Afghan forces in Kandahar this summer.

If the Taliban can be chased out of the Arghandab and kept out, the joint forces will turn toward battling militants in even more dangerous parts of Kandahar province to the south and west.

The battle for Kandahar originally was envisaged as a confrontation that could cripple Taliban fighters and compel their leaders to cut a peace deal with U.S.-backed Afghan President Hamid Karzai.

However, unforeseen delays and setbacks have forced the international military coalition to re-evaluate its plans. That, in turn, has cast doubt on President Obama’s pledge to begin scaling back the military operation next July.

While the specially trained police who are responsible for the new checkpoints are considered a cut above the conventional and widely disparaged Afghan police, U.S. soldiers say they need constant oversight.

NATO strategists are building about 17 checkpoints on the routes leading from Kandahar into the districts around the city where the Taliban built their power base.

The Taliban already have turned their sights on the security ring. On July 13, suicide bombers targeted the main Afghan police compound in Kandahar that’s responsible for the checkpoints.

The sophisticated attack killed three American soldiers, an Afghan police officer and three Afghan interpreters.

On a recent afternoon, cars heading out of Kandahar cut in front of listing trucks, and motorcyclists inched up the gritty pass toward the checkpoint.

On the opposite side, traffic from Arghandab ran smoothly as Afghan police waved through the trickle of vehicles on the road that runs into one of the most unstable, Taliban-friendly districts in Kandahar city.

One police officer sat in the shade of a building until his commander turned up with a reporter from McClatchy Newspapers.

“Stand up,” the commander shouted to the police officer. “They’re journalists. They’re taking pictures.”

In short order, the police officers began stopping every vehicle that was coming from Arghandab.

Besides choking off Taliban routes into Kandahar, the checkpoints are designed to persuade Afghans that the arrival of U.S.-trained forces will end endemic police corruption.

“It’s a systemic issue,” said British Maj. Gen. Nick Carter, commander of coalition forces in southern Afghanistan.

“We won’t change it, but if we can buy time for the people to think their government is generally trying to support them, then we might get them to work in this direction, as well.”

When that might happen and, more critically, whether it will happen in time to meet Obama’s timeline for withdrawing American forces, is unknown, however.