Tom DeLay has denied charges of money laundering and conspiracy

Lawyers for the former House majority leader told the Texas court that Bob Perkins had made contributions to Democratic candidates and causes.

They said the donations called his impartiality into question.

Congressman DeLay is accused of breaking campaign finance law, but denies the charges.

He is alleged to have laundered $190,000 (�108,000) in corporate contributions for use in Republican campaigns in Texas.

State law forbids the use of corporate money for political campaigns.

'Opposite sides'

Mr DeLay was until recently one of the most powerful politicians in Washington.

His lawyers argued that Judge Perkins' donations would create questions "in the minds of reasonable people" that he could not rule impartially.

They cited 34 contributions made to Democrats and groups since 2000, including donations to former presidential challenger John Kerry and the liberal group MoveOn.org.

"The public perception of Judge Perkins' activities shows him to be on opposite sides of the political fence than Tom DeLay," Dick DeGuerin said, according to the Associated Press.

Judge Perkins had declined to withdraw from the case and has said that he contributed to MoveOn.org only ahead of last year's presidential election.

Prosecutor Rick Reed argued that Mr DeLay must prove that a member of the public would have a "reasonable doubt that the judge is impartial" before Judge Perkins could be removed.

Mr DeGuerin said he was not accusing the judge of any wrongdoing.

But "to protect the integrity" of the judicial system, he should not preside over a trial for someone to whom he is opposed politically, Mr DeLay's lawyer said.

The judge in the hearing, CW Duncan, did not indicate who would replace Judge Perkins, nor when the trial would start.