WASHINGTON » When Shamai K. Leibowitz, an FBI translator, was sentenced to 20 months in prison last year for leaking classified information to a blogger, prosecutors revealed little about the case. They identified the blogger in court papers only as "Recipient A." After Leibowitz pleaded guilty, even the judge said he did not know exactly what Leibowitz had disclosed.

"All I know is that it’s a serious case," Judge Alexander Williams Jr., of U.S. District Court in Maryland, said at the sentencing in May 2010. "I don’t know what was divulged other than some documents, and how it compromised things, I have no idea."

Now the reason for the extraordinary secrecy surrounding the Obama administration’s first prosecution for leaking information to the news media seems clear: Leibowitz, a contract Hebrew translator, passed on secret transcripts of conversations caught on FBI wiretaps of the Israeli Embassy in Washington. Those overheard by the eavesdroppers included U.S. supporters of Israel and at least one member of Congress, according to the blogger, Richard Silverstein.

In his first interview about the case, Silverstein offered a rare glimpse of U.S. spying on a close ally.

He said he had burned the secret documents in his Seattle backyard after Leibowitz came under investigation in mid-2009, but he recalled that there were about 200 pages of verbatim records of telephone calls and what seemed to be embassy conversations. He said that in one transcript, Israeli officials discussed their worry that their exchanges might be monitored.

Leibowitz, who declined to comment for this article, released the documents because of concerns about Israel’s aggressive efforts to influence Congress and public opinion, and fears that Israel might strike nuclear facilities in Iran, a move he saw as potentially disastrous, according to Silverstein.

While the U.S. government routinely eavesdrops on some embassies inside the United States, intelligence collection against allies is always politically delicate, especially one as close as Israel.

The FBI listens in on foreign embassies and officials in the United States chiefly to track foreign spies, though any intelligence it obtains on other matters is passed on to the CIA and other agencies. The intercepts are carried out by the FBI’s Operational Technology Division, based in Quantico, Va., according to Matthew M. Aid, an intelligence writer who describes the bureau’s monitoring in a book, "Intel Wars," scheduled for publication in January. Translators like Leibowitz work at an FBI office in Calverton, Md.

Former counterintelligence officials describe Israeli intelligence operations in the United States as quite extensive, ranking just below those of China and Russia, and FBI counterintelligence agents have long kept an eye on Israeli spying.

For most eavesdropping on embassies in Washington, federal law requires the FBI to obtain an order from the Foreign Intelligence Surveillance Court, which meets in secret at the Justice Department. If an American visiting or calling an embassy turns up on a recording, the FBI is required by law to remove the American’s name from intelligence reports, substituting the words "U.S. person." But raw transcripts would not necessarily have undergone such editing, called "minimization."

Silverstein’s account could not be fully corroborated, but it fits the publicly known facts about the case. Spokesmen for the FBI, the Justice Department and the Israeli Embassy declined to comment on either eavesdropping on the embassy or Leibowitz’s crime. He admitted disclosing "classified information concerning the communication intelligence activities of the United States," standard language for the interception of phone calls, emails and other messages by the FBI and the National Security Agency, which generally focuses on international communications.

Leibowitz, now in a Federal Bureau of Prisons halfway house in Maryland, is prohibited by his plea agreement from discussing anything he learned at the FBI. Two lawyers who represented Leibowitz, Cary M. Feldman and Robert C. Bonsib, also would not comment.

Silverstein, 59, writes a blog called Tikun Olam, named after a Hebrew phrase that he said means "repairing the world." The blog gives a liberal perspective on Israel and Israeli-U.S. relations. He said he had decided to speak out to make clear that Leibowitz, though charged under the Espionage Act, was acting out of noble motives. The Espionage Act has been used by the Justice Department in nearly all prosecutions of government employees for disclosing classified information to the news media, including the record-setting five such cases under President Barack Obama.

Silverstein said he got to know Leibowitz, a lawyer with a history of political activism, after noticing that he, too, had a liberal-minded blog, called Pursuing Justice. The men shared a concern about repercussions from a possible Israeli airstrike on nuclear facilities in Iran.

Silverstein took the blog posts he had written based on Leibowitz’s material off his site after the criminal investigation two years ago. But he was able to retrieve three posts from April 2009 from his computer and provided them to The New York Times.

The blog posts make no reference to eavesdropping, but describe information from "a confidential source," wording Silverstein said was his attempt to disguise the material’s origin.

One post reports that the Israeli Embassy provided "regular written briefings" on Israel’s war with Hamas in Gaza to Obama in the weeks between his election and inauguration. Another describes calls involving Israeli officials in Jerusalem, Chicago and Washington to discuss the views of members of Congress on Israel. A third describes a call between an unnamed Jewish activist in Minnesota and the Israeli Embassy about an embassy official’s meeting with Rep. Keith Ellison, D-Minn., who was planning an official trip to Gaza.

Silverstein said he remembered that embassy officials talked about drafting opinion articles to be published under the names of U.S. supporters. He said the transcripts also included a three-way conversation between a congressman from Texas, a U.S. supporter of the congressman and an embassy official; Silverstein said he could not recall any of the names.

At his sentencing, Leibowitz described what he had done as "a one-time mistake that happened to me when I worked at the FBI and saw things which I considered were violation of the law, and I should not have told a reporter about it."

That was a reference to Israeli diplomats’ attempts to influence Congress, Silverstein said, though nothing Leibowitz described to him appeared to be beyond the bounds of ordinary lobbying.