Officers and analysts express concerns that some of these isolated units are falling prey to diminished standards of behavior and revert to what one combat veteran described as “Lord of the Flies” syndrome, after the William Golding novel portraying a band of cultured British schoolboys reverting to tribal violence when severed from society.

“Some of these incidents certainly seem to be the fault of a breakdown in leadership at the small-unit level,” said Andrew Exum, a defense policy analyst at the Center for a New American Security who teaches a course on irregular warfare at Columbia University .

“Where was the sergeant who is supposed to say: ‘Stop, boys. We don’t do that. We don’t disrespect the dead’?” said Mr. Exum, who led a light infantry platoon in Afghanistan in 2002 and then led a platoon of Rangers in both Iraq and Afghanistan in 2003 and 2004.

Early reports indicate that the soldiers had been sent to gather fingerprints or retina scans for identification of the suicide bomber. Mr. Exum noted how the horrific experience of being ordered to interact with bloody, severed body parts of an enemy may cause soldiers to develop self-defense mechanisms — in particular dark humor around corpses. “But the line is crossed when you disrespect the dead body,” he said. “It’s one thing to have a psychological release valve, and another thing to take trophy pictures.”

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Pentagon and military officials, noting that the proliferation of soldiers’ carrying camera phones has been involved in many of the cases, said that technology and a changing culture had presented new problems, as well. Troops have behaved badly since the beginning of warfare, of course. But now, those actions can be captured in real time, and spread rapidly without commanders’ control, via social networks.

Army officials said Wednesday that the service had guidelines and rules for photos — basically, “think before you post” — but they also acknowledged that social media are evolving so rapidly that regulations were not keeping pace. Rules are set by commanders at the company, battalion and brigade level, but those standards are sometimes ignored by small units in the field.

“Technology today presents definite challenges related to security and propriety,” said Col. Thomas W. Collins, an Army spokesman. “In this case, these photos are probably a manifestation of the soldiers’ relief that this insurgent no longer posed a threat to them or their fellow soldiers. That cannot excuse what they did. We are the United States Army , and the world rightly has very high expectations that our soldiers will do what’s right. Clearly, that didn’t happen in this case.”

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With more than a million military personnel having deployed overseas since the Sept. 11 terrorist attacks, the recent cases represent only a tiny percentage of the force. Senior American officials responding on Wednesday noted that, even as they condemned the soldiers’ behavior.

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“This is not who we are, and it’s certainly not what we represent when it comes to the great majority of men and women in uniform,” Defense Secretary Leon E. Panetta said at a NATO conference in Brussels , calling the soldiers’ behavior unacceptable and promising a full investigation. President Obama said that those responsible for the actions would be “held accountable,” and Gen. John R. Allen , the senior allied commander in Afghanistan, sounded similar themes. But Afghan officials described an increasing skepticism among the public after case after case of misbehavior has come to light over the past year.

Nadir Nadiry, an Afghan human rights activist in Kabul , said Afghans would likely react negatively because similar photographs had surfaced before and despite military investigations the latest pictures suggested that the actions continued to be perpetrated. “It gives them a sense of, ‘Oh they are continuing to do this,’ ” he said. “Each time they say they will conduct a thorough investigation, but these investigations are not being made public, so the results are not known to the Afghan people.”

Some Afghan officials said the behavior shown in the images was deeply offensive given Muslim views of how to treat dead bodies. Hajji Baz Mohammed, a tribal elder and head of the development council in Qalat, the capital of Zabul Province, where the soldiers were operating, told of how residents were enraged last year after a similar incident involved Afghan security forces.

“Eight months ago, Afghan security forces dishonored the bodies of two dead insurgents, which really infuriated the people here in Zabul,” he said. “People went to the streets, and three more went to the streets and three more died in the clashes between angry mobs and security forces.”

He added, “In the past episode, it was Afghans who insulted the bodies and three people were killed as a result — one can imagine what will happen if the people got to know that non-Muslims are insulting the dead bodies of Muslims.”

Several of the military analysts commenting Wednesday said the kind of lapses shown in the photos struck directly at the ability of American troops to perform their mission, given how important winning Afghans’ sympathies is to keeping the Taliban at bay.

Mr. Mohammed raised the same issue: “These kinds of acts would further increase the already widened gap between the people and the government, and would drive some government supporters toward the Taliban. In the meantime, it’s not good for the Americans: these kinds of acts would generate more hatred and would motivate people to vengeance.”