Tom DeLay is a close ally of President George W Bush

The judge said Mr DeLay's actions in the conspiracy charge were not a crime at the time that the alleged violations took place.

However, Mr DeLay remains accused of laundering corporate contributions for use in Republican campaigns in Texas.

The congressman has strongly denied both of the charges.

Texas state law forbids the use of corporate money for political campaigns.

'Politically motivated'

The ruling presents only a partial victory for Mr DeLay, who had hoped to reclaim his role as majority leader in the House of Representatives, which he gave up when indicted.

His spokesman Kevin Madden said the decision showed "how baseless and politically motivated the charges were".

"Mr DeLay is very encouraged by the swift progress of the legal proceedings and looks forward to his eventual and absolute exoneration based on the facts and the law," Mr Madden added.

The first judge assigned to the case was removed at Mr DeLay's request, after his lawyers said his Democratic ties called his impartially into question.

Mr DeLay and two others are accused of laundering $190,000 (�109,000) in corporate donations for distribution to Republican candidates to the Texas Legislature in the 2002 state campaign.