NEW ORLEANS — U.S. Attorney Jim Letten, whose successful prosecution of a former Louisiana governor and numerous other public officials won him bipartisan praise for more than a decade, resigned Thursday while the Justice Department investigates alleged misconduct by his top deputies.

Letten’s announcement was an abrupt end to his tenure as the nation’s longest-serving U.S. attorney. His crusade against crime resulted in convictions of corrupt judges, killer police officers, bribe-taking officials in New Orleans’ long-troubled school system and scammers who tried to rip off Hurricane Katrina aid programs. He first won fame as an assistant U.S. attorney leading the successful 2000 racketeering prosecution of former Gov. Edwin Edwards.

Letten didn’t address the allegations against his deputies during a news conference Thursday. He previously said that he had no idea what his deputies were doing until the online activity was revealed in court filings.

He said the decision to resign, effective Dec. 11, came after discussions with colleagues, Justice Department officials and his family. “The decision ultimately was mine.”

Dana Boente, the first assistant U.S. Attorney for the Eastern District of Virginia, was appointed in the interim. Attorney General Eric Holder said in a statement that Letten has been a “valued partner, dedicated public servant and a good friend.”

Letten didn’t take any questions from reporters before he left the room, kissing his wife and hugging tearful colleagues on his way out.

His success had made him one of the city’s most popular public figures, but his support among political officials in both parties diminished after revelations about the online activities of two veteran prosecutors in his office.

One, Sal Perricone, resigned in March after acknowledging he criticized judges and politicians and commented on cases in anonymous posts on a local newspaper’s website. Letten demoted his top assistant, Jan Mann, last month after she also confessed to posting anonymous comments on the same site.

The Justice Department’s Office of Professional Responsibility is investigating the matter.

The authors of the posts were unmasked in court filings by attorneys for New Orleans businessman Fred Heebe, whose landfill operations are the subject of a federal probe.

Letten has said he didn’t know about Perricone’s and Mann’s online posts until after Heebe’s court filings.

Heebe had been nominated by then-President George W. Bush for the U.S. Attorney position in November of 2001, but withdrew amid allegations that he had abused an ex-girlfriend and his ex-wife — allegations that he denied.

Letten was the acting U.S. attorney at the time. He held onto the post through the Bush years and was kept in what is often a political patronage position by Democratic President Barack Obama.

Letten is stepping down at a time when his office is ramping up an investigation of former New Orleans Mayor Ray Nagin’s administration. The probe already has resulted in guilty pleas by two businessmen who said they bribed an unidentified city official during Nagin’s tenure. It also has threatened to undermine other high-profile cases.

Last month, a federal judge ordered the Justice Department to conduct a new investigation of media leaks related to its probe of deadly police shootings on a New Orleans bridge after Hurricane Katrina. U.S. District Judge Kurt Engelhardt initially called for an investigation in June, but he said a report submitted by Mann is tainted and must be redone.

Engelhardt presided over a trial in which five former officers were convicted of civil rights violations stemming from the Danziger Bridge shootings. Defense attorneys have asked Engelhardt to order a new trial, arguing that media leaks deprived their clients of a fair trial.

Engelhardt urged the Justice Department to appoint a court-approved independent counsel to investigate the online posts and media leaks. On Thursday, Holder announced the appointment of John Horn, First Assistant U.S. Attorney for the Northern District of Georgia, to oversee the department’s new investigation of the matter.

U.S. Sen. Mary Landrieu, a Louisiana Democrat who has supported Letten even though he was initially appointed by a Republic president, said Letten’s record of rooting out public corruption should be commended despite the “troubling” allegations about his deputes. Landrieu said she will forward a short list of candidates to replace Letten to Holder and the White House in the coming weeks.