A retired engineer from New Jersey whose clandestine activities went undetected for more than two decades pleaded guilty yesterday to a criminal charge accusing him of serving as an unregistered agent for Israel.

Ben-Ami Kadish passed classified documents to an Israeli handler between about 1980 and 1985, when he worked at a U.S. Army research and engineering center at the Picatinny Arsenal in Dover, N.J., authorities say.

Kadish, 85, will face a maximum term of five years in prison when he is sentenced by Manhattan U.S. District Judge William H. Pauley III in February. The retiree acted out of a desire to help Israel, receiving only nominal gifts and family dinners in exchange for the 50 to 100 documents he shared, according to court papers filed by the government.

Kadish, a U.S. citizen born in Connecticut, checked classified papers out of an Army research library and passed them to an Israel official, identified for the first time by prosecutors yesterday as Yossi Yagur. Yagur photographed materials related to nuclear weapons, the F-15 fighter jet program and the U.S. Patriot missile defense system, according to court papers.

Yagur first drew attention more than 20 years ago as the handler for former Navy intelligence analyst Jonathan Pollard. Pollard is serving a life sentence in a federal prison in Butner, N.C., after pleading guilty in 1986 to an espionage-related charge.

Pollard's case became the subject of ongoing international furor, and some Israeli supporters continue to lobby for his pardon or early release from prison. But through all those years, Kadish remained well below the radar.

FBI agents arrived on Kadish's doorstep in a Monroe Township, N.J., retirement community in March 2008. Their visit prompted new contact in the form of a phone call between Kadish and Yagur, who left the United States more than two decades ago, prosecutors allege.

During the call, federal agents say, Yagur allegedly instructed Kadish to deny any involvement, saying: "Let them say whatever they want. . . . What happened 25 years ago? You didn't remember anything."

The next day, FBI agents questioned Kadish anew, and he denied the call had taken place, according to court filings. His statements restarted the espionage investigation and led to yesterday's guilty plea to a single conspiracy charge.

An attorney for Kadish and a spokesman for the Israeli Embassy did not return telephone calls.

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