Guilty plea expected in New York subway bomb plot

Najibullah Zazi is escorted by U.S. Marshals at a New York Police Department facility in Brooklyn, September 25, 2009.

NEW YORK (Reuters) - An imam accused of tipping off al Qaeda-trained militant Najibullah Zazi as he plotted to set off bombs in New York's subway system is expected to plead guilty to lying to the FBI, a court official said on Tuesday.

The official spoke on condition of anonymity.

Ahmad Afzali, 37, was arrested in September as part of a probe into what Attorney General Eric Holder called one of the most serious security threats to the United States since the September 11 attacks in 2001.

"It was in motion. And it would have been deadly," Holder has said.

The plea had been expected at a scheduled hearing on Tuesday but was delayed after prosecutors asked for the proceedings to be rescheduled for Thursday.

Afzali, who is out on bail, pleaded not guilty to the same charges in November. Reversing his plea may mean a deal has been reached with prosecutors.

Afzali's lawyer, Ronald Kuby, said his client had reached a deal with prosecutors but it has not yet been signed by all parties.

In what was hailed as a political victory for Holder, Zazi pleaded guilty in February to conspiracy to use weapons of mass destruction, conspiracy to commit murder in a foreign country and providing material support to al Qaeda.

Zazi moved to the New York City borough of Queens as a teenager and went to school there. He attended a mosque led by Afzali, a self-proclaimed pro-American imam who has cooperated with police in previous investigations.

Asked about Zazi, Afzali alerted him that he was under scrutiny, which forced authorities to bring Zazi in for questioning sooner than planned. Afzali lied about the tip-off when questioned by the FBI, prosecutors said.

Zazi's father, Mohammed Wali Zazi, also was expected to appear in Brooklyn federal court on Tuesday for a routine meeting.

(Reporting by Basil Katz; Editing by Ellen Wulfhorst and John O'Callaghan)