Democratic lawmakers are stepping up demands for an independent investigation into the still un-resolved leak to media last year of the name of a CIA officer. The renewed demands come as 10 former CIA employees sent a letter to Democrat and Republican leaders in Congress saying the unauthorized disclosure seriously damaged U.S. national security.

In a letter sent to congressional leaders of both parties, 10 former CIA analysts and officers call the disclosure of Valerie Plame's name "an unprecedented and shameful event in American history."

They say the leak "damaged U.S. national security, specifically the effectiveness of U.S. intelligence-gathering using human sources," and add that a thorough congressional investigation would "send an unambiguous message" that those working in the intelligence community must "never be turned into political punching bags."

Last year, a syndicated columnist, Robert Novak, published the name of Ms. Plame, who is married to former U.S. Ambassador Joseph Wilson, who has been critical of the Bush administration.

Mr. Wilson was thrust into the spotlight last year when he took issue with President Bush's use of information in his January 2003 State of the Union address about alleged Iraqi attempts to purchase "yellow-cake" uranium in the African nation of Niger.

In television interviews and appearances, he became a sharp critic of the Bush administration's handling of intelligence, noting that his own investigation in 2002, at the request of the Vice President Dick Cheney, determined that documents about the alleged purchase attempts were forgeries.

Mr. Wilson alleged that someone in the Bush administration then leaked the fact that his wife is a CIA agent, in an attempt to discredit his criticisms.

President Bush ordered an investigation into the leak, but in a statement last year said he thought it was unlikely that the person responsible would be found.

Democrats, including candidates for the 2004 Democratic party presidential nomination, focused on that comment accusing Mr. Bush of failing to recognize the damage done to U.S. intelligence.

House Democratic leader Nancy Pelosi Thursday renewed her call for an investigation independent of the probe the administration ordered.

For several months, a group of House Democrats led by Congressman Rush Holt has been demanding an open investigation into the leak, criticizing the Justice Department saying it should provide specifics of progress and a timetable for its conclusion.

Attorney General John Ashcroft has recused himself from the Justice Department investigation.

A day after President Bush's State of the Union Address, Mr. Holt, a member of the House Permanent Select Committee on Intelligence, introduced a "resolution of inquiry" asking for all documents relating to the leak of Ms. Plame's identity with the CIA.

Congress is required to act in some way on such a resolution within 14 days of its submission. However, it is thought unlikely the Republican leadership will agree to consider the resolution of inquiry.