President Bush's top advisers are not immune from congressional subpoenas, a federal judge ruled Thursday in an unprecedented dispute between the two political branches.

Congressional Democrats called the ruling a ringing endorsement of the principle that nobody is above the law. They swiftly announced that the Bush officials who have defied their subpoenas, including Bush's former top adviser Karl Rove, must appear as part of a probe of whether the White House directed the firings of nine federal prosecutors. Democrats announced plans to open hearings at the height of election season. The Bush administration was expected to appeal.

In his ruling, U.S. District Judge John Bates said there's no legal basis for Bush's argument and that his former legal counsel, Harriet Miers, must appear before Congress. If she wants to refuse to testify, he said, she must do so in person. The committee also has sought to force testimony from White House chief of staff Joshua Bolten.