Lieutenant Cobb, who did not testify at the trial, has been placed on modified assignment at the Police Department. She faces up to a year in prison, according to the district attorney’s office. Her lawyer declined to comment on the verdict.

The charges against Lieutenant Cobb stemmed from a brief meeting between her and two other city police officers at a tavern in Rockland County in 2010. Prosecutors contend that the lieutenant, who was working in the Internal Affairs Bureau at the time, nearly derailed the unfolding wiretap investigation by warning the two — Lt. William Kivlehan and Officer Kevin McCarthy — that the investigation had expanded into ticket-fixing and that officers’ conversations were being monitored.

Prosecutors said that her warning was subsequently passed along to police union officials, and that some police officers started using different phones or warning one another to discuss summonses in person. Donald Levin, an assistant district attorney, called Lieutenant Cobb “the Super Bowl of leaks” in the trial, saying the wiretap investigation almost collapsed as a direct result of her disclosure.

Lieutenant Cobb’s lawyers had sought to play down her role, saying that information about the investigation had already “leaked like a sieve.” They pointed out that Lieutenant Kivlehan, who is now a captain, and Officer McCarthy did not stop using the phone themselves to make tickets disappear, and recited a list of wiretaps that were set up in the months after the meeting in the tavern to suggest the investigation had continued to move forward.

Lieutenant Cobb is scheduled to be sentenced on Dec. 4.

Louis Turco, president of the Lieutenants Benevolent Association, who attended the hearing, said afterward that he was “extremely surprised” by the verdict. “We were extremely disappointed, obviously,” he said, “and we’re going to have a vigorous appeal of this verdict.”