WASHINGTON (Reuters) - A group of former CIA staffers is pushing for a congressional investigation into the "shameful" leaking of the name of undercover officer Valerie Plame, whose husband cast doubt on the Bush administration's claims about Iraqi weapons of mass destruction.

In a letter to U.S. House Speaker Dennis Hastert dated Jan. 20 and obtained by Reuters on Wednesday, 10 former CIA analysts and operatives called the disclosure of Plame's identity a "shameful event in American history" that had damaged national security.

"Congress must send an unambiguous message that the intelligence officers tasked with collecting or analyzing intelligence must never be turned into political punching bags," the letter said, saying such leaks jeopardized the work and safety of intelligence professionals and their sources.

The Justice Department is conducting an investigation into who leaked Plame's name to newspaper columnist Robert Novak last year.

Plame's husband, former diplomat Joseph Wilson, has accused administration officials of leaking her name in retaliation for his challenge to one of the reasons cited by President Bush for going to war against Iraq.

Wilson went to Niger early in 2002 at the CIA's request to assess a report that Iraq sought to buy uranium from Niger, but returned saying he had found no evidence to back the claim. The Niger allegation was later found to have been based partly on forged documents.

But it was mentioned in Bush's State of the Union speech in January 2003 to help build a case for war against Iraq. The White House has since admitted that Bush should not have included the charge, which he attributed to British intelligence, in his speech.

In their letter, the former CIA officers said a congressional investigation was important not only to uncover who leaked the name but also to signal that such behavior would not be tolerated.

U.S. Attorney General John Ashcroft has stepped aside from the Justice Department investigation and Bush has said the inquiry did not involve him "in any way, shape or form."

Separately, a group of Democrats led by Rep. Rush Holt of New Jersey on Wednesday introduced a "resolution of inquiry" that asks the president, Secretary of State, Secretary of Defense and Attorney General to give the House of Representatives all documents in their possession relating to the disclosure of Plame's identity.

The documents sought included telephone and electronic mail records, logs and calendars, personnel records, and records of internal discussions for the period May 6 through July 31 last year, a statement from Holt, who is a member of the House Intelligence Committee, said.

"Six months after a syndicated columnist disclosed the name of an undercover CIA operative, the White House and the Department of Justice have yet to find and hold accountable the person or persons who revealed her identity," Holt said.