WASHINGTON (Reuters) - Citing executive privilege, President George W. Bush on Wednesday rejected a subpoena for his close adviser Karl Rove to appear before to the Senate Judiciary Committee in a probe over fired federal prosecutors.

Deputy Chief of Staff and Senior Advisor to the President Karl Rove departs Air Force One in Philadelphia, July 26, 2007. REUTERS/Larry Downing

Bush’s move sets up a possible court showdown between the White House and Democratic lawmakers, who have sought to force Rove and other Bush aides to testify about the firing last year of nine federal prosecutors. Critics say they were fired for political reasons.

“Mr. Rove, as an immediate presidential advisor, is immune from compelled congressional testimony about matters that arose during his tenure and that relate to his official duties in that capacity,” White House Counsel Fred Fielding wrote in a letter to Senate Judiciary Chairman Patrick Leahy, a Vermont Democrat. Leahy made the letter available to Reuters.

“It is a shame that this White House continues to act as if it is above the law. That is wrong,” Leahy said in a statement. “The subpoenas authorized by this Committee in connection with its investigation into the mass firings of U.S. Attorneys and the corrosion of federal law enforcement by White House political influence deserve respect and compliance.”

The committee had subpoenaed Rove to testify at a hearing on Thursday morning, along with another White House aide, deputy political director Scott Jennings.

Rove will not appear at the hearing, while Jennings will appear but not testify about the fired prosecutors, Fielding said. Fielding also said the White House would not hand over documents requested by the committee.

Democrats say the firings may have been intended to influence investigations of Democratic or Republican lawmakers.

Bush and Attorney General Alberto Gonzales, who signed off on the firings, have said that they were justified but mishandled.

Gonzales also faces calls for a perjury investigation over the truthfulness of his testimony to Congress about the firings and the National Security Agency’s warrantless domestic-spying program.

With the support of Bush, Gonzales has rejected bipartisan calls to resign.

Gonzales said in a letter to Leahy he had been truthful with the committee last week when testifying about the surveillance program, which contains elements that remain classified.

“I was discussing only that particular aspect of the NSA activities that the President has publicly acknowledged,” Gonzales wrote. “I recognize that ... my shorthand reference to the ‘program’ publicly ‘described by the President’ may have created confusion.”

At least one member of the committee was unsatisfied with the explanation.

“The Attorney General has done far more than create confusion, he’s placed his office in disrepute,” New York Democratic Sen. Charles Schumer said in a statement. “After reading the letter, we renew our call for a special prosecutor with vigor.”