Mr. Abramoff is believed to have extensive knowledge of what prosecutors suspect is a wider pattern of corruption among lawmakers and Congressional staff members. One participant in the case who insisted on anonymity because of the sensitivity of the negotiations described him as a "unique resource."
Other people involved in the case or who have been officially briefed on it said the talks had reached a tense phase, with each side mindful of the date Jan. 9, when Mr. Abramoff is scheduled to stand trial in Miami in a separate prosecution.
What began as a limited inquiry into $82 million of Indian casino lobbying by Mr. Abramoff and his closest partner, Michael Scanlon, has broadened into a far-reaching corruption investigation of mainly Republican lawmakers and aides suspected of accepting favors in exchange for legislative work.
Prominent party officials, including the former House majority leader, Representative Tom DeLay of Texas, are under scrutiny involving trips and other gifts from Mr. Abramoff and his clients. The case has shaken the Republican establishment, with the threat of testimony from Mr. Abramoff, once a ubiquitous and well-connected Republican star, sowing anxiety throughout the party ranks.
At issue is the complicated structure of the case against Mr. Abramoff. In August, he was indicted by federal prosecutors in Miami on charges of fraud stemming from his purchase of a fleet of casino boats in 2000. He pleaded not guilty in that case, and his lawyers say they are preparing him to stand trial. Mr. Abramoff has also been under investigation here in connection with his lobbying. No charges have been brought against him in that inquiry. The existence of what amounts to two separate but overlapping investigations partly explains why the plea negotiations for Mr. Abramoff have been so protracted and tough, said people with inside knowledge of the case.
With the trial in Miami fast approaching, and coming on the heels of plea agreements from Mr. Scanlon and another close associate of Mr. Abramoff, pressure has mounted to reach his own agreement. Mr. Abramoff has also told associates that he is broke, making the prospect of an extended jury trial even less appealing.
Mr. Abramoff's the lead defense lawyer, Abbe D. Lowell, said he would not comment.
Several people involved in various aspects of the case agreed to be interviewed as long as their names and affiliations were not made public. Justice Department officials are prohibited from discussing continuing cases as a matter of course. A spokesman for the department, Bryan Sierra, declined to comment.
Although the Miami case is ostensibly separate from the Washington inquiry, the overlapping elements include occasions when Mr. Abramoff flexed his political muscle to enhance his business deal in Florida.
While he and a partner, Adam Kidan, were angling to buy the SunCruz boat fleet in 2000, Mr. Abramoff had Mr. Scanlon persuade Representative Bob Ney, Republican of Ohio, to insert negative comments about a business rival of Mr. Abramoff into The Congressional Record, under to a scheme outlined in documents filed in Mr. Scanlon's criminal case.
The rival, Konstantinos Boulis, was murdered a short time later in Fort Lauderdale, Fla., a twist that heightened the profile of the Miami case.
Florida prosecutors are also investigating corruption in that case, focusing on Mr. Ney and his chief of staff at the time, Neil Volz, according to people involved in the case. Mr. Volz reportedly agreed to put negative remarks about Mr. Boulis in The Congressional Record, even though Mr. Ney had no obvious reason to comment on Mr. Boulis.
Mr. Volz went on to work for Mr. Abramoff as a lobbyist.
Mr. Ney has said he was tricked by Mr. Scanlon and Mr. Abramoff into participating, and no charges have been brought against him.
In his financial paperwork in the Miami deal, Mr. Abramoff listed Tony C. Rudy, a deputy chief of staff to Mr. DeLay at the time, as a reference.
He also listed Representative Dana Rohrabacher, Republican of California, who has since defended the decision to support the lobbyist.
Lawyers for Mr. Volz, Mr. Ney and Mr. Rudy did not return calls for comment. A lawyer for Mr. DeLay declined to comment, but spokesmen for Mr. DeLay have repeatedly said he had done nothing improper.
Such ties are only at the periphery of the investigations, according to people briefed on the case. Mr. Scanlon, who worked on public affairs for the SunCruz casinos and is familiar with the inner workings of many of Mr. Abramoff's deals, is cooperating in the Miami case as well as in Washington, his lawyer has said.
Prosecutors are also looking at how some former Congressional staff members landed their lucrative lobbying positions and at the role the wives of several lobbyists and lawmakers may have had in any influence scheme, a piece of the puzzle that investigators have begun referring to privately as the "wives' club."
