NEW YORK, July 23 (Reuters) - A U.S. man has pleaded guilty to helping al Qaeda plan an attack on New York's Long Island Rail Road and to firing rockets at U.S. troops in Afghanistan, a court transcript unsealed on Thursday showed.

Bryant Neal Vinas, 26, from Long Island, also admitted at a Brooklyn federal court hearing on Jan. 28 that he trained with the Islamist extremist group, according to the transcript, which was unsealed after a media request.

Vinas faces a maximum sentence of life in prison. A date for sentencing has not been set, a court official said.

"I consulted with a senior al Qaeda leader and provided detailed information about the operation of the Long Island Rail Road system which I knew because I had ridden the railroad on many occasions," Vinas told the court.

"The purpose of providing this information was to help plan an ... attack on the Long Island Rail Road system," he said.

Vinas told Judge Nicholas Garaufis that he left Long Island late in 2007 and traveled to Pakistan with the intention of joining a jihadist group to fight U.S. troops in Afghanistan.

"I made contact with and was accepted into al Qaeda," he said. "As a member of al Qaeda, I received training in courses in general combat and explosives.

"I took part in firing rockets at an American military base. Although we intended to hit the military base and kill American soldiers, I was informed that the rockets missed and the attack failed," Vinas said.

New York's Metropolitan Transportation Authority, which operates the Long Island Rail Road, said it had been in constant contact with authorities as the investigation developed and that there "was never an imminent threat to the system."

The Long Island Rail Road describes itself as the busiest commuter railroad in North America, carrying more than 300,000 passengers every weekday. (Reporting by Grant McCool, Writing by Michelle Nichols; Editing by Xavier Briand)

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