WASHINGTON — The tighter the U.S. military and Afghan allies cinch the noose around supporters of Osama bin Laden, the greater the danger of American troops getting killed, the Pentagon chief said Friday.

Defense Secretary Donald H. Rumsfeld portrayed the Taliban militia and al-Qaida fighters as giving ground, being backed into a corner and creating confusion even as many surrender or change sides.

``Let there be no doubt, there will be further casualties in this campaign, in Afghanistan and elsewhere,'' Rumsfeld said on the 55th day of the U.S. aerial assault that has punished but not finished off the Taliban.

The only substantial portion of Afghanistan still under Taliban control is the area around Kandahar, the southern city that gave birth to the radical Islamic movement. Marine Corps Gen. Peter Pace said at a joint news conference with Rumsfeld that the military situation there was unclear.

``We do not know what we cannot see, which is how many actual fighters there are inside the city,'' Pace said. ``There has not yet been a major ground offensive battle. There are, we know, negotiations going on between the opposition forces and the Taliban leadership for surrender.''

There are still pockets of resistance elsewhere in Afghanistan, and Rumsfeld said there are thousands of Taliban and al-Qaida fighters being held prisoner by the northern alliance and other opposition forces. It is difficult to determine who among the prisoners are Taliban or al-Qaida leaders without questioning them directly — a situation that exposes the interrogators to danger, he said.

``They are people who, for the most part, don't walk up and volunteer their names and identification numbers with a sample of DNA,'' Rumsfeld said. ``What they do is, they blend into the other prisoners.''

This was the situation last weekend when CIA officer Johnny ``Mike'' Spann was killed while interrogating enemy prisoners in Mazar-e-Sharif, a northern city under the control of the northern alliance, Rumsfeld said. He praised Spann as a hero who knew the risks he faced.

A military transport will bring Spann's body home to his family Sunday, CIA officials said. He was shot and killed Sunday.

Rumsfeld said the Taliban and al-Qaida are still dangerous, even as their hold on Afghanistan crumbles.

``The Taliban can no longer freely move around the country; they're finding it increasingly difficult to manage their remaining forces,'' Rumsfeld said. ``Ironically, however, as the size of the Taliban real estate diminishes, the danger to coalition forces may actually be increasing.'' That is largely because shifting allegiances and growing chaos make it hard to distinguish friend from foe.