AN AMERICAN journalist at the centre of a scandal over the leaking of a CIA official’s identity revealed yesterday that her source was the chief of staff of Dick Cheney, the US Vice-President, increasing pressure on the White House to explain its role in the affair.

After nearly three months in jail for her refusal to testify before a grand jury investigating the leak, Judith Miller, of The New York Times, was released on Thursday night. She named I Lewis “Scooter” Libby, Mr Cheney’s closest adviser, as the official who had spoken to her about Valerie Plame, the CIA agent in question. Her move reignited a politically charged investigation that has already ensnared Karl Rove, President Bush’s chief political adviser.

It has been a damaging week for the White House, rocked by the criminal indictment of the Republicans’ House leader Tom DeLay, ethics investigations of other senior Republicans, and the repercussions of the Hurricane Katrina disaster.

Ms Miller, 57, told the grand jury that she had met Mr Libby on July 8, 2003, six days before Ms Plame was first identified in an article by the conservative columnist Robert Novak.

Ms Miller said her decision to testify came after she had personally received, in a call to her jail ten days ago, an explicit waiver from Mr Libby releasing her from any obligation to conceal his identity.

His lawyer, Robert Tate, said that Ms Miller had been told a year ago that she was free to testify, but Ms Miller said yesterday that she had never received a personal assurance from Mr Libby. Democrats asked how Ms Miller could have been allowed to languish in a federal prison for 85 days before the matter was cleared up.

The White House had, until recently, maintained for nearly two years that Mr Libby and Mr Rove were not involved in leaking the identity of Ms Plame, whose husband, Joseph Wilson, a former US Ambassador, had accused the Bush Administration of “twisting” intelligence before the Iraq war.

The controversy has its roots in a CIA-sponsored trip Mr Wilson made to Niger in 2002 to investigate reports that Iraq had tried to buy uranium there. In July 2003 Mr Wilson asserted that the White House’s prewar Niger claim was bogus. A week later Mr Novak revealed Ms Plame’s identity. He wrote that Ms Plame, a CIA agent, had suggested her husband for the trip, citing “two senior administration officials” as sources.

Mr Wilson said the Bush Administration was trying to punish him by destroying his wife’s career. He claimed his wife was an undercover CIA operative whose life was now in danger.

Three days after Mr Novak’s article appeared, Matthew Cooper, of Time magazine, wrote that “some Administration officials” had told him that Valerie Plame was a CIA official.

It is a crime knowingly to reveal the identity of a covert agent. In September 2003 the Justice Department began an investigation. Mr Bush’s spokesman said that Mr Rove and Mr Libby were not involved.

The investigation by Patrick Fitzgerald, the special prosecutor, has included interviews with Mr Bush, Colin Powell, the former Secretary of State, Mr Rove and Mr Libby.

Mr Cooper told the grand jury in July that Mr Rove had first told him about Ms Plame. Mr Cooper said that he had spoken to Mr Rove three days before Mr Novak’s column appeared. He said Mr Rove told him Mr Wilson’s wife worked at the CIA, and that information was about to be released to discredit Mr Wilson. Mr Cooper said he also spoke to Mr Libby about the matter.

Mr Cooper said Mr Rove did not disclose Ms Plame’s name or suggest he knew she was a covert agent. Although Ms Miller investigated the claims, she did not publish a story about them.

There is no public evidence to suggest that Mr Rove or Mr Libby committed a crime and questions remain over whether Ms Plame was an undercover agent. Last year Mr Bush pledged to anyone who leaked Ms Plame’s name.

Last night Ms Miller said that she hoped her time in jail would strengthen bonds between reporters and their sources and that a federal law would be passed “so the public’s right to know will be protected”.

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