The U.S. and its NATO allies last week set a goal of starting to transfer control of Afghanistan to the central government by the end of the year, and President Obama has said U.S. troops must start leaving in 2011.
But the slow pace of progress makes it less likely Obama can meet these tight deadlines, and it's not clear if he can buy more time: He has struggled to persuade Congress to commit troops based on the current schedule.
The expanded U.S. campaign began in late winter in the small farming hamlets of Marjah, in Helmand Province, and has advanced more slowly than expected, officials said.
Now U.S. and NATO troops face a much more formidable task: securing Kandahar, the birthplace of the Taliban and the area from which al Qaeda planned the Sept. 11 terrorist attacks.
Gen. Stanley McChrystal, the top commander in Afghanistan, has described the campaign in Afghanistan's south as a slowly rising tide that will require time and patience. He and other military officials also have warned of an inevitable rise in casualties.
"I think we've been very clear for months now that this was going to be a very difficult fight in the south, and tried to set expectations, as tragic as it is, for these losses," Adm. Mike Mullen, Obama's top military adviser and head of the Joint Chiefs of Staff, recently told reporters.
The drive this summer to secure Kandahar was supposed to build on the success of the much smaller Marjah operations.
But so far the U.S. and NATO haven't achieved their goals in Marjah, military and civilian officials said, as the government has been slow to provide services and villagers have not rallied in large numbers to the Kabul-based government.
"We're still moving forward more slowly than the people would like," Mark Sedwill, NATO's senior civilian representative, said on a trip to Marjah this month.
Sedwill still sees overall progress, and other civilian reconstruction specialists said it was unrealistic to expect a smoothly operating local government little more than two months after the initial assault on Marjah.
Two senior Pentagon officials who visited Marjah in recent weeks said the Marines who provide the backbone of security in the district are not getting enough tips from the villagers or spending enough time with local leaders.
People are hanging back, afraid to throw their lot with the government even if they hate the Taliban, military officials said, and the opportunity to win their trust is fading.
The officials spoke on condition of anonymity because they weren't authorized to speak publicly.
The worry among military strategists is that if their tactics don't take hold in Marjah, with a population of roughly 80,000, what will happen in Kandahar?
The site of heavy fighting with the Soviets in the 1980s, Kandahar became a command post and spiritual homeland for the Taliban and al Qaeda in the 1990s before the 2001 NATO-led invasion.
If they are not aiding the Taliban directly, Kandahar's 1 million-plus inhabitants are seen as sympathetic toward the militants and skeptical of the new Afghan government.
U.S. special operations forces already have begun arriving in districts surrounding Kandahar's city center, focusing on districts where the Afghan central government has little or no authority.
This June, NATO and the United States plan to greatly expand military operations in Kandahar after the bulk of the 30,000-troop buildup ordered by Obama arrives.
The goal is to make significant headway by August, when the holy month of Ramadan begins. Military officials are betting that the spike in violence and casualties will abate by summer's end, and the Taliban's grip on the city will be loosened.
There are currently 7,800 NATO troops in the region, operating along side some 12,000 Afghan soldiers and police. By early summer, NATO forces should swell to 11,200.
The difficulty of the fight to come was illustrated Monday, when the United Nationsin Kandahar to stay home following a wave of violence.
Several foreign U.N. employees were temporarily moved to Kabul hours after three bombings - one aimed at a top police official - shook the city and left two civilians dead.
Worried last year that the Taliban was regrouping, NATO ordered reinforcements to the Arghandab Valley and other areas in and around the city to bolster a small group of Canadian forces in the area.
More recently, checkpoints have been opened around the city and special operations forces are moving closer. A senior military official in Kabul said more than 70 Taliban leaders have been "taken off the streets" in recent months.