The New York Times and associated press

WASHINGTON – Hundreds of Marines landed at a makeshift airfield near the southern city of Kandahar on Sunday in the first major infusion of U.S. grounds troops into Afghanistan. Their arrival began what Pentagon officials said would be a period of sustained assaults against Taliban and al-Qaida forces.

The Marines were to be the front edge of a powerful force of more than 1,000 combat troops who, the officials said, will join the hunt for Osama bin Laden within days, and then begin raids against Taliban forces concentrated in Kandahar and in mountain redoubts near the border with Pakistan.

The arrival of U.S. troops came as the Northern Alliance claimed to have seized Kunduz, the Taliban’s last northern stronghold, after a two-week siege.

The fall of Kunduz, which came two days before talks were to begin in Germany on forming a broad-based government, leaves the Islamic militia with only a small slice of Afghanistan still under its control, mostly around Kandahar.

Thousands of Taliban troops as well as Arab, Chechen, Pakistani and other foreign fighters linked to Osama bin Laden had been holed up in Kunduz, which the alliance said fell almost without a fight.

Pro-Taliban fighters including foreigners fled Sunday toward the town of Chardara, to the west, with alliance troops in pursuit, alliance acting foreign minister, Abdullah, said by satellite telephone from the north of Afghanistan.

While some chose to make a run for it, thousands of others surrendered by the thousands as Northern Alliance troops moved in. Under a pact negotiated earlier between the alliance and the Taliban, Afghan Taliban fighters were guaranteed safe passage out of the city but the foreigners were to be arrested pending investigation into possible ties to bin Laden.

Outside the city of Mazar-e-Sharif, 100 miles to the west, hundreds of foreigners who had been captured earlier in the Kunduz area staged a prison uprising, leading to a daylong battle with Northern Alliance guards. U.S. aircraft helped quash the insurrection.

In the south, immediately upon landing in CH-53 and CH-46 transport helicopters, the Marines set to work securing the airstrip, 12 miles southeast of Kandahar, the Taliban’s political base and last major military stronghold. The officials said that C-130 cargo planes carrying additional troops, armored vehicles and supplies were expected to begin landing at the field within 24 hours.

They said the advance party of Marines, members of the 15th and 26th Marine Expeditionary Units, encountered no resistance when they landed shortly after nightfall.

The arrival of the Marines confirmed the shift in the U.S. strategy from using air power and proxy Afghan armies to oust the Taliban, to relying on powerful U.S. forces which can, as Defense Secretary Donald Rumsfeld put it, “crawl around on the ground and find people.” Even in that role, though, the Marines will still receive heavy air support, as well as assistance from Western allies.

With their superior firepower – the Marines bring armored personnel carriers, Cobra attack helicopters and Harrier jump jets – they will be more heavily armed and more mobile than previous U.S. ground troops in Afghanistan, capable of conducting sustained and repeated assaults across a much larger geographic area, Pentagon officials said.

In total, the two Marine units based on ships in the Arabian Sea have about 4,400 troops, basically a brigade of ground forces with its own helicopters, fighter planes and artillery. It is not clear how many of them eventually will go ashore.

The Marines would probably not roam the countryside in search of enemy forces, as special operations forces have been, but would instead be dispatched on clearly focused missions guided by clear and credible intelligence reports, military officials said.