"Bob gave a personal reason for his resignation," said spokesman Bryan Sierra. He stressed that Coughlin "had no involvement" in the department's investigation of Abramoff.

Coughlin had worked in the criminal division since 2005 but was recused from the Abramoff inquiry because of a longtime personal friendship with Kevin A. Ring, one of Abramoff's lobbying colleagues whose actions are under investigation, a law enforcement source said. Investigators are looking into dealings between the two in 2001 and 2002, when Coughlin worked in the Justice Department's Office of Legislative and Intergovernmental Affairs, the sources said.

Coughlin and Ring were friends on Capitol Hill in the 1990s when both worked as staffers to then-Sen. John D. Ashcroft (R-Mo.), who became attorney general in 2001.

Coughlin's resignation and the surfacing of his name in the Abramoff investigation were first reported yesterday by McClatchy Newspapers.

Investigators came across Coughlin's name while looking into whether Ring improperly sought or received favors for lobbying clients from people in government, the sources told The Washington Post.

Ring took Coughlin to sporting events with tickets provided by his lobbying firm, according to sources familiar with the inquiry.

The task force has tracked millions of dollars in meals, trips, tickets, gifts and campaign contributions that the Abramoff lobbying team lavished on lawmakers and staffers. The investigation has so far resulted in 11 convictions and guilty pleas from lobbyists, staffers, two administration officials and a congressman.

An attorney for Ring could not be reached for comment. Coughlin did not answer calls to his home yesterday, and a lawyer who is serving as his spokesman did not return phone calls seeking comment.

Coughlin is the second Justice Department official whose name has surfaced in the wide-ranging Abramoff investigation. Earlier this year, Sue Ellen Wooldridge, deputy assistant attorney general for environment and natural resources, abruptly resigned when her boyfriend -- now her husband -- was notified that he was a criminal target. J. Steven Griles, former deputy secretary of the Interior Department, has since pleaded guilty to lying to Congress about Abramoff.