They're facing guerrillas who were born here, hardened by poverty and backwardness, and steeped in a centuries-old tradition of resisting foreigners. The guerrillas' aim is to impose another hard-line Islamic regime on Afghanistan, one that might make the country once again a sanctuary for Osama bin Laden and his al-Qaida jihadis.

The Taliban have killed more than 40 U.S. soldiers and more than 800 Afghan officials, police, troops, aid workers and civilians since March in a campaign aimed at derailing Sept. 18 parliamentary and provincial elections and eroding confidence in President Hamid Karzai and his American-led backers.

Borrowing tactics from their counterparts in Iraq, they've beheaded alleged informers and staged two suicide bombings, a form of terrorism rarely seen in Afghanistan.

The fighters of the resurgent Taliban movement are no match in face-to-face clashes for highly trained U.S. troops, who are equipped to fight at night and are backed by helicopter gunships, jets, unmanned spy planes, Afghan soldiers and local intelligence officers.

But after suffering massive casualties in a series of major firefights, the Taliban have learned to avoid set-piece battles with the U.S. and Afghan troops who are trying to pen them up in the mountains so they can't sabotage the upcoming polls.

The war has evolved into a bloody game of cat and mouse, a classic guerrilla struggle with echoes of the much larger and far bloodier conflicts in Iraq, Chechnya and Vietnam.

The outcome may well come down to which side can outlast the other.

The Taliban operate in small bands, staging hit-and-run attacks, assassinations and ambushes, laying mines and firing missiles and rocket-propelled grenades before melting back into local populations. U.S. intelligence reports indicate that Taliban leaders constantly change locations.

"One day, they could be firing at you and serving you chai (tea) the next," said Army Capt. Michael Kloepper, 29, of Caldwell, N.J., after a helicopter dropped him and some of his men on a boulder-strewn hilltop dubbed Landing Zone North Dakota on a two-day mission in a remote valley in southern Zabul province.