A jazz musician from the Bronx pleaded guilty yesterday to pledging to use his martial arts training to help Al Qaeda.

Tarik Shah emerged at the center of a wide-ranging terrorism sting operation that involved an FBI agent who posed as a recruiter for Al Qaeda.

In the presence of the agent, Shah swore fealty to Osama bin Laden in 2005, according to the indictment. As part of that oath, taken in a Bronx apartment, Shah promised to train Al Qaeda operatives in hand-to-hand combat, prosecutors said. That offer became the basis of the charges filed against him in U.S. District Court in Manhattan. Yesterday’s guilty plea was to conspiring to provide material support to a terrorist organization, a crime for which Shah faces 15 years in prison.

Prosecutors said they have evidence that Shah, 44, had long intended to support jihadists overseas. He had said he tried to attend a military training camp in Afghanistan in 1998, according to government court filings.

In addition to Shah, the sting operation also resulted in the arrests of three of Shah’s friends. Two of them, a paramedic from Maryland and an Islamic bookseller from Brooklyn, have already pleaded guilty to criminal charges. The Maryland man, Mahmud Brent, attended a terrorist training camp in Pakistan, and the bookseller, Abdulrahman Farhane, conspired to send money to jihadists in Afghanistan and Chechyna.

Shah said little at yesterday’s hearing, beyond admitting that he knew supporting Al Qaeda was “wrong.” Nonetheless, during questioning by a prosecutor, Karl Metzner, the defendant appeared unwilling to call Al Qaeda a terrorist organization. After consulting with his lawyer for several minutes, Shah conceded only that he knew the government considered Al Qaeda to be a terrorist organization.

Since his arrest in May 2005, Shah has railed against the conditions of his imprisonment, which include solitary confinement. In an impassioned letter filed to the court last year, he demanded a hearing to review his solitary confinement on the grounds that he is a “an American with well over ten generations of family who were also American.”

In return for the guilty plea, prosecutors are dropping charges that he conspired with the Islamic bookseller in Brooklyn to wire money to jihadists overseas.

The remaining case from the sting operation involves a Columbia-educated doctor who most recently lived in Florida. The doctor, Rafiq Sabir, is charged with pledging to provide medical treatment to Al Qaeda operatives wounded in training. Mr. Sabir, a close friend of Shah’s, is alleged to have made similar pledge in support of Mr. bin Laden in the presence of the same undercover agent.