Washington - Twenty former US attorneys, both Republicans and Democrats, urged a federal judge Thursday to intervene in a constitutional battle over whether two White House officials should be forced to testify before Congress about the firings of nine U.S. attorneys.

    The former top prosecutors, including two who served under President Bush, argue in court papers that the judge should reject the Bush administration's assertion of blanket immunity for presidential chief of staff Joshua Bolten and former White House counsel Harriet Miers in the congressional investigation.

    Democrats in the House of Representatives say they were forced to sue in March, more than a year after they launched the probe, because the administration has refused to allow Miers and Bolten to provide crucial information about the reasons the prosecutors were fired. The case also could determine how former presidential adviser Karl Rove responds to a subpoena in a related congressional investigation.

    The lawsuit accuses administration officials of injecting partisan considerations into the firing decisions and making "questionable or outright false statements" in subsequent explanations to Congress.

    The prosecutors acknowledged that the administration could have legitimate legal reasons for not allowing Bolten and Miers to testify. However, they called on U.S. District Judge John D. Bates to weigh Congress' arguments carefully because of the serious nature of the allegations.

    "This congressional inquiry involves the possible subversion of principles at the core of Constitutional government," they wrote. "It is a matter of the utmost importance for Congress to conduct a complete investigation to determine whether White House officials have injected, or attempted to inject, partisan considerations into a process that must be rigorously insulated from such considerations."

    The administration has denied any wrongdoing and maintains that Congress has no compelling interest to review White House deliberations on the matter.

    The prosecutors who voiced support for Congress' position include officials who served under presidents Johnson, Nixon, Carter, Reagan, Clinton and both President Bush and his father, former president George H.W. Bush.

    Alan Bersin, a former U.S. attorney under Clinton, and William Braniff, a former U.S. attorney under George H.W. Bush, both served as the top federal prosecutor in San Diego, where the Bush administration later fired then-U.S. attorney Carol Lam. Former New Mexico U.S. Attorney David Iglesias, who was among the ousted prosecutors, and Matthew Orwig, a former U.S. attorney under Bush in Beaumont, Texas, also signed the brief.

    "This brief is apolitical and legally sound," said Orwig, who was described in internal Justice Department documents that came out during the controversy as a "loyal Bushie." "It was clear as this controversy unfolded that the reasons given for the firings were fabricated. It also became clear that the congressional investigation was being impeded."

    Four legal and watchdog organizations also filed briefs in support of Congress: the Brennan Center for Justice at New York University School of Law, the Rutherford Institute, Judicial Watch, and Citizens for Ethics and Responsibility in Washington.

    The congressional investigation into the firings of the U.S. attorneys produced suspicions but no proof that the prosecutors were targeted because they'd rebuffed Republican demands that they bring weak voter-fraud cases against Democrats or because they'd mounted corruption investigations of Republicans.

    Although White House and Justice Department officials have acknowledged the firings were handled badly, they've insisted the ousters weren't orchestrated to hinder or encourage certain prosecutions. A spokesman for the Justice Department declined to comment on the latest developments in the lawsuit.