WASHINGTON — Jack Abramoff, the Republican lobbyist who may be facing an array of fraud and corruption charges, has been talking with prosecutors about a deal that would grant him a reduced sentence in exchange for testifying against former political and business associates, people with detailed knowledge of the case have said.

What began as a limited inquiry into $82 million of Indian casino lobbying work by 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, Tom DeLay of Texas, are under scrutiny involving trips and other gifts from Abramoff and his clients. The case has shaken the Republican establishment, with the threat of testimony from Abramoff, once a ubiquitous and well-connected Republican star, sowing anxiety throughout the party ranks.

In August, Abramoff 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. Abramoff has also been under investigation in Washington 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 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 Scanlon and another close associate of Abramoff, pressure has mounted to reach his own agreement. Abramoff has also told associates that he is broke, making the prospect of an extended jury trial even less appealing.

Abramoff's lead defense lawyer, Abbe D. Lowell, said he would not comment.