Naeem Koochi, an Afghan tribal leader with a large and loyal following, was nearing the capital late last month on his way to a meeting with top government officials when two unmarked vehicles pulled up beside him and at least five men jumped out, waving pistols and automatic rifles.

The men, who weren't in uniform but appeared to be Americans, yanked Koochi out of his car and pushed him into theirs, according to Afghan witnesses. They sped off to the U.S. air base at Bagram, north of Kabul, and Koochi has not been heard from since.

Two weeks later, the capture and incarceration of a top elder of one of the largest tribes in the Pashtun ethnic group has brought hundreds of other elders here to plead for his release. Perhaps more importantly, Koochi's high-profile detention has stirred Afghans to do something that hundreds of similar arrests by U.S. forces have not: protest that American soldiers are abusing their position by detaining Afghans in their own country without consulting local officials, without any legal process and without even an explanation.

"To have Afghan citizens picked up on Afghan streets by American forces, with no reasons given and no rights, that is not looked on kindly by the Afghan nation," said Hashmat Ghani, the leader of the council of Koochi's Ahmadzai tribe.

"This is what we expected during the Soviet time here, not with the Americans," he said.

Afghan President Hamid Karzai, whose government is supported by the United States, has told Koochi's supporters that he strongly favors their demand that he be freed. But Koochi has not been released or even allowed to talk to other Afghans, despite Karzai's intercession.

U.S. military officials would not confirm that Koochi is at the Bagram base, but Lt. Gen. Daniel McNeill, who runs the American war effort from there, said on Friday that U.S. forces want to question him. He said the war on terrorism requires that people who are possible threats to U.S. forces and those of other nations be apprehended whenever possible.

"I will simply say that he was taken into custody and there is some fairly good information connecting him to things and people whose activities, and capabilities to carry out these things, probably are working to the detriment of the coalition," McNeill said. "We'd simply like to know more about what he knows."

The capture of Koochi comes at a time when the U.S. government is working hard to enhance the image of the Karzai government as one that controls its own affairs. But Koochi's detention offers fresh evidence that it does not, and the fact that the U.S. military has such a free hand concerns some human rights advocates.

"Americans are in charge in Afghanistan, and the military's position seems to be they can do whatever they want," said John Sifton, an Afghan specialist with Human Rights Watch. "There doesn't appear to be any legal principle -- really, any principle at all -- that limits what they can do."

Sifton said his organization has not followed the Koochi case but knows that many Afghans have been imprisoned for much longer than Koochi has been, and without any apparent procedure in place to determine how their cases will be handled. "It's an absolutely terrible situation, because people have no way to assert a claim of innocence," he said.

In the absence of such a process, members of the Ahmadzai tribe are bringing political pressure on the Afghan government and U.S. officials. If Koochi is not released soon, Ghani said, the Ahmadzai will protest to the United Nations and through other nonviolent means. He said the Ahmadzai, who number more than a million in Afghanistan, will insist on a resolution of the issue.

By most accounts, Koochi, believed to be about 60, has a checkered past. He is the unofficial leader of the nomadic Koochi clan of the Ahmadzai, though not a nomad himself, and was active both as an Islamic guerrilla fighting Soviet occupation with U.S. backing in the 1980s and as a leading commander of the Taliban Islamic militia. Under Taliban rule, he was governor of Bamian province at a time of fierce fighting.

After the fall of the Taliban in late 2001, Koochi was told to check in regularly with Ghani and to make himself available to U.S. forces for questioning. According to Ghani, Koochi complied and even played a significant and constructive role in the popular assembly, or loya jirga, that elected Karzai president last summer. When Koochi worked with the Taliban, Ghani said, he did so out of necessity, like many tribal leaders, and was eager to support Karzai when he became leader.

"Nobody can swear 100 percent that another person is innocent, but I know him well and he has kept to a regular schedule of coming to speak with me," said Ghani, whose brother is Ashraf Ghani, a former World Bank official who is now Afghan finance minister and is highly respected by many Americans in Kabul.

Koochi's apparent desire to show support for Karzai brought him into almost fatal contact with U.S. forces in December 2001. Koochi was in a group of elders traveling from southeastern Afghanistan to Kabul for Karzai's inauguration as appointed leader when U.S. warplanes -- acting on intelligence that many have concluded was intentionally incorrect -- bombed the convoy and killed a number of men, including a nephew of Koochi. Ghani said he believes the Americans are once again acting against Koochi on the basis of misinformation.

Others familiar with the case are not as sure that Koochi has given up his Taliban past. A top Afghan official said the United States had potentially damaging information about Koochi's recent actions and was checking it out.

As Afghanistan begins its second year since the fall of the Taliban, dealing with men such as Koochi is complicated for both the United States and Karzai's government.

There is no doubt that Koochi was an active Taliban leader and that he and his clan live in the eastern provinces, where U.S. soldiers searching for remnants of the Taliban and al Qaeda are frequently attacked. On the other hand, not only does he have a large following among the Ahmadzai, whose cooperation is essential to the war against al Qaeda and the Taliban, but he also is representative of the many Taliban leaders and followers who did not flee the country after their government was toppled and who want to resume their lives.

In a guesthouse in Kabul, several dozen older men -- wrapped in blankets and wearing the large turbans of the Pashtun tribes -- expressed anger and hurt that Koochi had been captured and not released.

"Yes, Naeem Koochi was with the Taliban before, but now he is leading a peaceful life," said Ghulam Khan, who came in from Paktia province, a day's ride to the southeast. "This is something for the Afghan government, not for the Americans."

"This arrest makes the Karzai government look very weak," said another elder, Mir Sardar, from Khost. "We appreciate the help from Americans, but this is making Afghans very mad at them."

Compounding the sense of hurt, they say, is the way Koochi was arrested -- considered very disrespectful, since he was not fleeing -- and the difficulty Afghans have had contacting U.S. officials. The U.S. Embassy in Kabul is a fortress that is hard to approach without encountering a rifle-toting Marine, and Bagram air base is off-limits to aggrieved Afghans.

"Afghans know Americans have the power to capture anyone they like," said Mohammad Ali Jalali, governor of Paktika province on the Pakistani border, who supports the effort to free Koochi. "Most Afghans have supported the Americans, and I hope the United States does not do things now to make Afghans hate them in the future."

McNeill asked for patience in the Koochi case and others like it. "The elders of this group see only a certain side of him," McNeill said. "I have information on both sides of him. If any turns out not to be true, I will have very little interest in him, and he's likely to be none the worse for the wear, and his people are likely to be none the worse for the wear."

"I have not only an obligation to the coalition," McNeill said, "but we are doing our dead level best to help the Afghans make their country more secure and stable."