WASHINGTON (Reuters) - Democratic lawmakers on Wednesday subpoenaed Secretary of State Condoleezza Rice to testify about a central and later refuted administration justification for the 2003 U.S.-led invasion of Iraq.

Secretary of State Condoleezza Rice speaks to President Bush during a ceremony honoring the Super Bowl Champion Indianapolis Colts at the White House, April 23, 2007. REUTERS/Jim Young

But the administration said it might fight the subpoena, citing a legal doctrine that can shield a president and his aides from having to answer questions from Congress.

“Those matters are covered by executive privilege,” said State Department spokesman Sean McCormack, moving toward a possible legal showdown with the Democratic-led Congress.

On a party-line vote of 21-10, the House of Representatives’ Oversight and Government Reform Committee approved a subpoena for Rice, which was quickly issued.

It directs her to answer questions from the panel next month about the administration’s claim -- later proven false -- that Iraq had sought uranium from Niger for nuclear arms.

“There was one person in the White House who had primary responsibility to get the intelligence about Iraq right -- and that was Secretary Rice who was then President George W. Bush’s national security adviser,” said committee Chairman Henry Waxman, a California Democrat.

“The American public was misled about the threat posed by Iraq, and this committee is going to do its part to find out why,” Waxman said.

The claim about Niger was a major factor in the administration’s case for war, and critics later accused the White House of having twisted intelligence to build support. The administration denies it.

Rep. Tom Davis of Virginia, ranking Republican on Waxman’s committee, accused Democrats of going on a “fishing expedition.”

Davis noted that a number of previous investigations had concluded that the claim about Niger “reflected the broadly supported state of knowledge at that time.”

WHITE HOUSE SCRUTINY

Waxman said there had been investigations about mistakes within the intelligence community, but he wanted to determine “what went wrong inside the White House.”

The subpoena for Rice was part of a flurry of action on Wednesday in the stepped-up congressional oversight of how the Bush administration operates. Since Democrats took control of Congress from Bush’s Republicans in January, there have been more than 400 oversight hearings.

“There is a difference between oversight and over-reaching,” said White House spokeswoman Dana Perino.

The House Judiciary Committee voted to authorize a subpoena of Monica Goodling, a former Justice Department official, and seek a court order of immunity for her in its probe of the firing last year of eight of the 93 U.S. attorneys.

“Taking this step will compel her to testify, under penalty of contempt,” said Judiciary Committee Chairman John Conyers, a Michigan Democrat seeking to determine if the dismissals were politically motivated.

Goodling had earlier invoked her right against self-incrimination in refusing to testify before the Senate Judiciary Committee.

The Senate Judiciary Committee, which grilled Attorney General Alberto Gonzales last week about the ousted prosecutors, authorized a subpoena for Sara Taylor of the White House office of political affairs.

Bush has vowed to oppose any attempt to compel sworn congressional testimony from White House aides in the investigation of the ousted prosecutors. Gonzales contends that the firings were justified, but mishandled.