(Adds details of plea agreement and background in paragraphs 3-8)
WASHINGTON, Sept 23 (Reuters) - A former FBI agent has agreed to plead guilty to leaking secret government information about a bomb plot to a news agency, a leak that Attorney General Eric Holder called one of the most serious in U.S. history, the Justice Department said on Monday.
As part of a plea agreement filed in U.S. District Court in Indiana, Donald John Sachtleben agreed to a prison sentence of three years and seven months for the leak in addition to a separate sentence for unrelated child pornography charges, the department said.
A lawyer for Sachtleben, 55, of Carmel, Indiana, did not immediately respond to a request for comment.
A story by the Associated Press in May 2012 described a U.S. operation in Yemen to foil a plot to bomb an airliner. The AP said it delayed publishing the story at the request of government officials until security concerns were allayed, but U.S. officials said the leak compromised a U.S. agent working to undermine the Islamic militant group al Qaeda in the Arabian Peninsula.
Two months later, Attorney General Eric Holder appointed a senior prosecutor to lead an investigation.
Sachtleben retired from the FBI in 2008, after about 25 years, according to the Justice Department. He continued to work on contract as a bomb analyst.
According to a copy of a plea agreement dated Sept. 6 and released on Monday, Sachtleben agreed to plead guilty to one count of unauthorized disclosure of national defense information and one count of unauthorized possession and retention of national defense information.
If accepted by a judge, the prison sentence would be the longest ever handed down in a civilian court for a leak of classified information to a reporter. (Reporting by David Ingram; Editing by Howard Goller, Sandra Maler and Eric Walsh)