KANDAHAR, Afghanistan — For weeks now, the men in black turbans have been coming. They travel in pairs or small groups, on battered motorbikes or in dusty pickups, materializing out of the desert with Kalashnikovs and rocket launchers slung from their shoulders.

With the advent of warmer weather, villagers say, Taliban fighters are filtering back from their winter shelters in Pakistan, ensconcing themselves across Afghanistan’s wind-swept south.

“Every day we see more and more of them,” a farmer who already had sent his family away for safety, Abdul Karim, said.

The insurgents aren’t the only ones girding for battle.

At the country’s main NATO base outside Kandahar, nearly 2,300 American Marines have arrived over the past two months, their presence heralded by the thunder of transport aircraft and the springing up of a tent city built on a newly cleared minefield.

The Marine force’s final elements arrived days ago and began fanning out into the field, aiming to bolster British, Canadian, and Dutch troops who until now have been bearing the brunt of fighting in Afghanistan’s south, considered the conflict’s strategic center.

The conflict in Afghanistan dominated discussions at last month’s NATO summit, where President Bush pledged to send more troops and pointedly urged allies to do likewise. Earlier this year, Defense Secretary Gates heard urgent appeals for reinforcements from American commanders in Afghanistan, who forecast a substantial surge in fighting.

In Afghanistan, where presidential elections are due next year, opinion surveys consistently suggest that a majority of the population supports the presence of foreign forces. But people don’t want them to stay indefinitely.

The first-time arrival in Afghanistan’s south of a large force of Marines, the 24th Expeditionary unit based in Camp Lejeune, N.C., has provided what commanders say is a much-needed infusion of firepower. The Marines have doubled the coalition’s air capacity; rows of Harrier jump jets, lumbering cargo planes, and combat helicopters line the freshly laid tarmac.

Just as important, commanders say, the Marines’ deployment might give NATO-led troops the muscle and reach to choke off the flow of Taliban fighters and weaponry into neighboring Helmand province, consistently the most violence-racked in Afghanistan. [Yesterday, two attacks were launched against Afghanistan’s vulnerable police, killing eight officers, including four who were destroying a field of opium poppies, officials said, according to the Associated Press.

Kandahar provincial police chief Sayed Agha Saqib said the militants killed four eradication police in the province’s Maiwand district on Saturday. ]