John Walker Lindh was full of religious fervor when he stepped off the plane on his first trip to the Middle East.

But the brand of Islam that the "American Taliban" encountered in Yemen apparently wasn't zealous enough for him.

A baptized Roman Catholic who converted to Islam at 16, Lindh traveled alone to Yemen at 17 in the summer of 1998.

He donned white robes and sandals, wore a full beard, and even pretended to speak broken English with an Arabic accent before abandoning the school where his parents had paid thousands of dollars for a year's stay in Yemen.

He insulted other Muslims and repeatedly got into trouble with authorities, say those who encountered the California teenager.

Lindh objected to having women in his classes, according to students and administrators at the school where he studied Arabic.

Frustrated with the school, he sought more fundamentalist teachings in the country's dangerous northern mountains, but was repeatedly turned back by Yemen's military, said Steven Hyland, who taught English and studied Arabic at the Yemen Language Center.

"This is an individual whose idealism led to ideology and he lost all ability for pragmatic thought," Hyland said by telephone from Texas.

Lindh, now 20, was captured in November fighting on the side of the Taliban in Afghanistan.

He first embarrassed his school, situated in the capital of San'a, the morning after his arrival in Yemen.

He exchanged several hundred dollars — a substantial sum in a country where the average civil servant earns about $75 a month. On his way back from the money market, Lindh saw beggars and decided to pay alms to the poor, one of the five pillars of Islam.

"When you give money to beggars in the street, you give them about 10 rials," Hyland said. "He starts passing out 200 rial notes, which is way, way, way too much."

Lindh was mobbed. A woman who worked at the school had to break up the crowd to protect the young American.

"John is in the middle of this whirlwind of people," Hyland recalled. "He's much taller than the average Yemeni, with a fist full of cash just raised in the air with his left hand and with his right hand just duking the Yemenis away."

After that incident, Lindh told other students he was disenchanted with aspects of Yemeni culture and began skipping classes at the school, where about 15 language teachers instruct four or five students each in several elegant buildings near the city's center.

"From that point on, Yemenis weren't Muslims, and that was the argument that he tried to make," Hyland said.

Josh Mortensen, another student, said from Cairo that Lindh asked peers to call him Suleiman, affected a "bogus" Arabic accent and wore traditional Muslim garb unlike that of most Yemenis. Other foreign students at the school mockingly nicknamed him "Yusuf Islam," the name pop singer Cat Stevens took when he became a Muslim and rejected his music career.

"That whole convert thing just doesn't compute for lifelong Muslims. It's almost like they're being made fun of in a way," Mortensen said. "He was so clueless and so rigid, and it was almost patronizing. He adopts all these ridiculous stereotypes."

Lindh slipped up again by approaching another student, Rizwan Mawani, who happens to be a Shia Muslim, and asking for directions to a Sunni mosque. Lindh was adamant about not wanting to pray with Shiites, who are part of the other main branch of Islam.

"I wasn't insulted. I found it quite humorous," Mawani recalled in a telephone interview from London. In Yemen, Mawani said, Shia and Sunni Muslims typically pray side by side.

Lindh was frustrated when he saw some Yemeni Muslims ignoring the calls to prayer, students said. He was particularly bothered when Mawani told Lindh he was more interested in taking a nap, Mawani recalled.

Mawani said Lindh considered himself a Salafi, part of a movement whose members believe they are promulgating the true Islamic faith as taught by the prophet Muhammad in seventh-century Arabia.

"Yemenis speak one of the purist forms of Arabic, but it's not a fanatical country," said Barbara Bodine, U.S. ambassador at the time. "Somebody looking for that fire-and-brimstone approach would get to Yemen and be very unhappy. It's simply not there."

The language center's owner, Sabri Saleem, said Lindh disappeared after complaining that his classes included women and that the secular school did not offer the Islamic studies he craved.

Lindh's goal, other students said, was to reach the mountains of northern Yemen, a risky venture for an American teenager. Militants there have kidnapped or killed numerous Western tourists.

"John was problematic for the center because he kept trying to steal away to the northern part of the country because there was an Islamic theologian there that he wanted to study under," Hyland said.

Saleem, interviewed by telephone recently while visiting the United States, said Lindh did not surface until police caught him at the airport months later. He had overstayed his visa and failed to get an exit visa.

Lindh came home to Marin County, north of San Francisco, in the spring of 1999. Eight months later, he returned to Yemen, then went to Pakistan and then Afghanistan, where he fought with the Taliban. Now he is being held by the U.S. military as the Bush administration decides how to deal with him.

Lindh's parents referred all questions to their lawyer, James Brosnahan. His spokeswoman had no comment on Lindh's stay in Yemen.

Islamic experts said that in his naivete, Lindh, a baptized Roman Catholic who converted to Islam at 16, fell into a trap so common that Muhammad himself predicted it.

"A person who might have been living a typical happy-go-lucky life and then he really gets very much attracted to the teaching of Islam and its ideal, but then he wants to change overnight — that's what the prophet actually was teaching against," said Jamal Badawi of the Islamic Information Foundation in Halifax, Nova Scotia. "He said, 'Go gently."'

The Associated Press contributed to this report.