Lawrence Franklin, an analyst in the office of the secretary of defence, pleaded guilty in October to sharing the information and to having classified documents at his home, actions provoked by his concern over the perceived threat from Iran.
Franklin had faced a prison sentence of up to 25 years but his term was reduced by district judge T S Ellis because of the defendant's cooperation and it could be cut further he helps with the case against two remaining defendants scheduled for trial in April, a condition of his plea bargain.
Ellis said: "The defendant did not seek to hurt the United States. He thought he was helping to bring certain information to the attention of the security council."
Franklin did not speak at Friday's sentencing, but said at his plea hearing in October that he was motivated by frustration with US policy in the Middle East when he gave classified information to Israeli diplomat Naor Gilon and lobbyists, Steven Rosen and Keith Weissman from the American Israel Public Affairs Committee (AIPAC) between 2002 and 2004.
Since that time concerns over Iran have been heightened due to Tehran's plans for nuclear research.
"I see some element of personal ambition"
Judge T S Ellis
Franklin admitted that he met periodically with Rosen and Weissman and discussed classified information, including information about potential attacks on US troops in Iraq.
He said he believed that Rosen and Weissman's contacts on the security council could help advance a tougher stance against Iran.
The 12-year, 7-month sentence imposed was on the low end of federal sentencing guidelines. Prosecutors had said a sentence within the guidelines was appropriate.
Element of ambition
Prosecutor Kevin DiGregory said Franklin's actions were dangerous because "once the U.S. government loses control of classified information, there's no way of knowing into whose hands that information may fall."
Ellis also said on Friday that he does not believe Franklin's motives were entirely altruistic. The judge cited court records that show Franklin asked Rosen to advocate on his behalf when Franklin was under consideration for a job at the security council. "I see some element of personal ambition" in Franklin's actions, the judge said.
Rosen was a top lobbyist for Washington-based AIPAC for more than 20 years, and Weissman was the organisation's leading expert on Iran.
Lawyers for Rosen and Weissman have argued that the pair were engaged in routine lobbying work and their discussions with Franklin are protected under First Amendment guarantees of free speech.
AIPAC dismissed Rosen and Weissman in April and says it has cooperated with the investigation.