WASHINGTON — One of the government's witnesses against convicted Sen. Ted Stevens of Alaska says he didn't tell the truth on the stand about an immunity deal with the Justice Department in exchange for his testimony.

"I testified to the fact that there was never immunity for me or my family and friends," welder David Anderson said in a letter to a federal judge placed in court files by Stevens' lawyers Friday. "That is simply not true."

Stevens' lawyers have asked U.S. District Judge Emmet Sullivan to hold a hearing on Anderson's charges and to let them investigate it. It was not immediately known when Sullivan would make a ruling.

The Justice Department had no immediate comment.

Stevens, 85 and the Senate's longest-serving Republican, was convicted on seven felony counts of lying on Senate financial documents to hide hundreds of thousands of dollars in gifts and home renovations from millionaire businessman and VECO founder Bill Allen, who is Anderson's uncle.

The senator, who won't be sentenced until early 2009, has said he will appeal the conviction. He lost his Senate seat to Democratic challenger Mark Begich in the November election.

Stevens gave his farewell speech to the Senate on Thursday, telling his colleagues: "I look only forward and I still see the day when I can remove the cloud that currently surrounds me."

Anderson supervised the start of the 2000 renovation of Stevens' Girdwood, Alaska, home and later responded to maintenance requests by Stevens and his wife. He testified at the trial that a March 2008 affidavit he signed that would give immunity to his family and friends in exchange for his testimony was false.

"That was never said," Anderson testified on Oct. 9. "It was kind of a gentleman's agreement, you know."

In his letter, Anderson said: "The agreement was that if I cooperated my entire family would be safe from the investigation(s) of the Department of Justice and also the Treasury Department. The Department of Justice has never ever denied that they shook my hand on this agreement but instructed me on how to sugar coat it and get it swept under the rug during the trial as they have told the court just the opposite."

Anderson also said he was given extensive help by the prosecutors in remembering events surrounding the renovation of Stevens' house.

"Without the preparation from the prosecution and reminders from them about my activities and the agreement I had with them about my family and myself I would not have given the same testimony," Anderson said. "Without a shadow of a doubt I believe this trial would have gone much differently."