Four years ago, a studious California teenager named John Philip Walker Lindh startled his middle-class Catholic parents by announcing that he was converting to Islam. A few days ago, after a long and still mysterious journey abroad to study the religion, he turned up on an Afghanistan battlefield as a bloodied Taliban fighter who called himself Abdul Hamid.

Bearded and bedraggled, with a gunshot wound to his leg, the 20-year-old told U.S. military officers and journalists that he had fought alongside the Taliban for months, until he and other fighters surrendered to Northern Alliance forces last week.

And he may not be the only American to have joined the Taliban. Two other captured soldiers also claim to be U.S. citizens, a senior U.S. defense official said in Washington.

"I have seen military reporting saying that there are two other Americans in [Northern Alliance] custody -- Americans believed to have been fighting for the Taliban," the official said. "I can't tell you their names or where they are, but I have seen that in military reporting."

Frank Lindh and Marilyn Walker, who are separated and live in the San Francisco suburbs, identified their son after a close family friend taped CNN footage on his capture and showed it to them. The family moved to California about 10 years ago from Silver Spring.

"They couldn't believe it," Bill Jones, the family friend, said today. "He's a good American kid. He had been on a spiritual quest and they were supportive. They broke into tears when they heard him called an 'American Taliban.' He must have got swept away in something, because he was on a mission of mercy."

In a CNN interview shown today, Walker, who was born in the District and uses his mother's last name, said he became acquainted with the Taliban while studying Islam in Pakistan and that his "heart became attached" to some of the group's fundamentalist teachings. He also told Newsweek that he left Pakistan to join the Taliban in Afghanistan about six months ago to help build a "pure Islamic state." Reporters who have spoken with Walker said he plainly looks and sounds like an American.

Jones said that Walker had been overseas for several years and that his parents had last heard from him in the spring, when he sent an e-mail from Pakistan. "They had been trying everything to track him down," Jones said.

Walker was captured with Taliban forces in the northern Afghan city of Mazar-e Sharif, and he was among a small number of survivors in an uprising by prisoners that took the life of a CIA officer last week. He emerged from the basement of a mud-walled fortress that had been turned into a makeshift prison, giving up only after Northern Alliance troops poured in oil and set it alight, then fired rockets into the underground tunnels and finally flooded them with cold water.

Pentagon officials said today that the Northern Alliance had turned Walker over to U.S. military forces and that he was receiving medical attention for his wounds. But Rear Adm. John Stufflebeem, deputy director of operations for the Joint Chiefs of Staff, would not say whether Walker was considered a prisoner of war.

"The only thing that I can say about this individual is that this is somebody who claims to be an American citizen," Stufflebeem said. "That claim is being respected at the moment."

Tonight Frank Lindh, who once worked as a Justice Department lawyer in Washington, told CNN's "Larry King Live" that until his son disappeared this spring he had no reason to believe that he was doing anything but zealously pursuing religious studies overseas.

He said he was horrified by what had happened to his son, but added that he also wanted to give him a "little kick in the butt for not telling us what he was up to."

Over the weekend, Lindh told Newsweek that Walker -- who was named after the late Beatle John Lennon -- became intrigued with Islam after reading "The Autobiography of Malcolm X" in high school and later dropped out to study the religion full-time. "He was exceptionally devoted to his studies," Lindh said. Marilyn Walker, a home health care worker who is a convert to Buddhism, told the magazine that her son often had spoken about returning to the United States to study medicine so he could help the poor in countries such as Pakistan.

The couple said that when they last heard from their son seven months ago, he did not seem different. He said he was studying the Koran and did not discuss any political issues or express anger with America, though he said he planned to go "somewhere cooler" for the summer. He also asked for money, and his father sent him $1,200.

His mother called him "a sweet, shy kid" and expressed shock that he had been fighting for the Taliban.

"He must have been brainwashed," she told Newsweek. "He was isolated. He didn't know a soul in Pakistan. When you're young and impressionable, it's easy to be led by charismatic people."

Before moving to California, the family lived near University Boulevard in Silver Spring, in a neighborhood of brick homes and tall oaks.

Today, former neighbors remembered the couple and their three children as quite friendly and described Walker as a normal, fun-loving boy who attended Kensington-Parkwood Elementary School in Montgomery County.

"We played together as long as he lived here," said Andrew Cleverdon, 19. "He was a regular kid. Me and him were rambunctious. Our parents were always yelling at us for being loud and obnoxious."

Another neighbor, Christina Reichel, a retired IBM sales executive, described the family as devout Catholics who went to Mass every Sunday. Both Frank Lindh and Marilyn Walker were "very well-educated and intellectual," she said. "I'd describe the whole family as intellectually curious, very thoughtful and very philosophical, always interested in new ideas."

Walker apparently has been overseas for most of the past three years, first studying Arabic in Yemen and later enrolling in a religious school in a Pakistani village.

Lindh told Newsweek that the only hint of his son's changing political attitudes came in an e-mail exchange shortly after terrorists detonated a bomb next to the destroyer USS Cole, an attack that killed 17 American sailors in Yemen in October 2000. He said his son suggested that the bombing may have been justified because the ship was docked in an Islamic country.

In a brief interview with CNN after his capture, Walker said the time he spent at an Islamic school in Pakistan's Northwest Frontier Province drew him close to the Taliban. People in that region, he said, "in general have a great love for the Taliban, so I started to read some of the literature of the scholars, the history of Kabul. . . . My heart became attached to it."

Jones, the family friend, said such comments suggest that Walker has been profoundly transformed since he left California. "He wasn't following any political agenda back then," Jones said. "It was like he was going off to start his own little Peace Corps."

Staff writers Annie Gowen and Vernon Loeb and researchers Margot Williams and Margaret Smith contributed to this report.

Taliban volunteer John Phillip Walker Lindh.Television footage from Mazar-e Sharif, Afghanistan, shows injured American, right, who calls himself Abdul Hamid.Taliban fighter John Phillip Walker Lindh is a native of the District who grew up in Silver Spring, moved to California and converted to Islam in his teens.