Washington, D.C. ? A federal judge on Thursday rejected President Bush’s contention that senior White House advisers are immune from subpoenas, siding with Congress’ power to investigate the executive branch and handing a victory to Democrats probing the dismissal of nine federal prosecutors.

The unprecedented ruling undercut three presidential confidants who have defied congressional subpoenas for information that Bush says is protected by executive privilege. Democrats swiftly announced they would schedule hearings in September, at the height of election season.

House Speaker Nancy Pelosi said the House could soon vote on a contempt citation against one of the three officials, Karl Rove, formerly Bush’s top adviser.