House Democrats called the ruling a ringing endorsement of the principle that nobody is above the law.
In his ruling, U.S. District Judge John Bates said there is no legal basis for Mr. 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.
"Harriet Miers is not immune from compelled congressional process; she is legally required to testify pursuant to a duly issued congressional subpoena," Bates wrote. He said that both Bolten and Miers must give Congress all non-privileged documents related to the firings.
The ruling is a blow to the Bush administration's efforts to bolster the power of the executive branch at the expensive of the legislative branch. Disputes over congressional subpoenas are normally resolved through political compromise, not through the court system. Had Mr. Bush prevailed, it would have dramatically weakened congressional authority in oversight investigations.
The administration can appeal the ruling.
The leader of the House of Representatives, Speaker Nancy Pelosi, a Democrat, called it "very good news for anyone who believes in the Constitution of the United States and the separation of powers, and checks and balances."
Democrats swiftly pledged to call Miers before the Judiciary Committee as soon as September to testify about whether the White House played any role in the firings of nine U.S. attorney's last year.
Judiciary Committee Chairman John Conyers, a Democrat, said he hoped that Miers and Bolten do not appeal the ruling, but that was far from clear.
White House spokesman Tony Fratto and Justice Department spokesman Peter Carr said they were reviewing the opinion and declined immediate comment.
Nonetheless, Conyers signaled election-season hearings will be held on the controversy that scandalized the Justice Department and led to the resignation of a longtime presidential confidant, Attorney General Alberto Gonzales.
"We look forward to the White House complying with this ruling and to scheduling future hearings with Ms. Miers and other witnesses who have relied on such claims," Conyers said in a statement. "We hope that the defendants will accept this decision and expect that we will receive relevant documents and call Ms. Miers to testify in September."
Bates, who was appointed to the bench by Mr. Bush, issued a 93-page opinion that strongly rejected the administration's legal arguments. He noted that the executive branch could not point to a single case in which courts held that White House aides were immune from congressional subpoenas.
"That simple yet critical fact bears repeating: the asserted absolute immunity claim here is entirely unsupported by existing case law," Bates wrote.