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The White House denied on Monday that President Bush's top political adviser leaked a CIA (search) agent's identity to retaliate against an opponent of the administration's Iraq policy. Prodded by Democrats, the Justice Department said it was looking into whether a full investigation was warranted -- a step rarely taken.

Two months after the CIA complained that the identity of an undercover agent had been exposed in apparent violation of the law, the Justice Department's counterespionage section is still conducting a preliminary probe, officials said. The White House was cool toward Democrats' argument that a special counsel should be appointed to guarantee an impartial investigation.

The disclosure of the intelligence officer's identity by syndicated columnist Robert Novak came shortly after her husband, former Ambassador Joseph C. Wilson (search), undermined Bush's claim that Iraq had tried to buy uranium in Africa. In what turned out to be a major embarrassment, Bush was eventually forced to acknowledge he could not back up his statement.

The controversy over leaking was the latest Iraq-related problem for Bush, along with the administration's failure to find Saddam Hussein (search) or the weapons of mass destruction that Bush cited as justification for waging war in Iraq.

The White House said that leaking classified information was a serious matter that should be "pursued to the fullest extent" by the Justice Department. "There's been nothing, absolutely nothing brought to our attention to suggest any White House involvement, and that includes the vice president's office as well," presidential spokesman Scott McClellan said.

In particular, McClellan said it was "ridiculous" to suggest that Karl Rove, Bush's top political operative, was involved, as once alleged by Wilson. "He wasn't involved," McClellan said of Rove. "The president knows he wasn't involved. ... It's simply not true."

Four Senate Democrats, including Minority Leader Tom Daschle, urged Attorney General John Ashcroft to appoint a special counsel, a person of "unquestioned independence and impartiality."

"We do not believe that this investigation of senior Bush administration officials ... can be conducted by the Justice Department because of the obvious and inherent conflicts of interests involved," said the letter, also signed by Sens. Carl Levin, D-Mich., Joseph Biden, D-Del. and Jay Rockefeller, D-W.Va.

The Justice Department receives about 50 CIA referrals a year seeking a preliminary investigation into leaks of classified information, a senior administration official said. Very few ever get beyond the preliminary investigation.

Investigators have to answer a number of questions before deciding whether to begin a full-blown criminal investigation, the official said. Among the most difficult to determine is how many people in the government might have been privy to the classified information. Other key questions are how much damage was done by disclosure, whether the leaker was aware the information was classified and whether that person had intended to violate the law.

The Justice Department is operating under no deadline for action, the official said, speaking on condition of anonymity.

White House officials, at their senior staff meeting, were urged to contact Justice if they had relevant information, officials said.

Novak said in a televised interview that his report was based on conversations with two senior administration officials while he was looking into Wilson's trip to Africa to investigate the uranium story. The officials told Novak that Wilson's wife had suggested the mission for her husband, the columnist said.

He said the CIA confirmed her role and "asked me not to use her name, but never indicated it would endanger her or anybody else."

Wilson backtracked Monday, saying he had not meant to imply that Rove "was the source or the authorizer, just that I thought that it came from the White House, and Karl Rove was the personification of the White House political operation."

But Wilson also said, in a telephone interview, "I have people who I have confidence in, who have indicated to me that he [Rove], at a minimum, condoned it and certainly did nothing to put a stop to it for a week after it was out there."

From Capitol Hill to the presidential campaign trail, Democrats called for the appointment of a special counsel.

"A crime was committed here, a very serious crime," said Sen. Charles Schumer, D-N.Y.

After Novak's column was published, the CIA's Office of General Counsel sent a letter in late July to the Justice Department, saying that a violation of the law had apparently occurred when someone provided Novak with the CIA officer's name. The letter was not signed by CIA Director George Tenet and did not call for a specific investigation of the White House.

McClellan said White House officials were not trying to determine on their own what had happened or who was involved. "Are we supposed to chase down every anonymous report in the newspaper? We'd spend all our time doing that."

Asked about the appointment of a special counsel, he said, "There are a lot of career professionals at the Department of Justice that address matters like that. ... It wouldn't be our place to get involved in that."

The rules for appointment of a special counsel give Ashcroft wide latitude to either appoint one outright, conduct a preliminary investigation to determine if such a counsel is needed or to conclude that it would be better for the Justice Department to handle the probe itself.

Among the rivals for Bush's job:

-- Former Vermont Gov. Howard Dean said Ashcroft should recuse himself from an investigation, which Dean said should be handled by an "independent Justice Department inspector general."

-- Rep. Dick Gephardt, D-Mo., called for a congressional investigation. "I don't think we can leave this to the administration's own Justice Department," he said.

-- Sen. Joe Lieberman, D-Conn., said an independent, non-partisan counsel should investigate. "It would be scandalous if such acts were a reaction to the public's conclusion that the president has used 16 misleading words in his State of the Union address last January."

-- Sen. John Kerry, D-Mass., also called for a special counsel. "Too many questions exist to risk allowing any potential for political intervention," he said.

-- Sen. John Edwards, D-N.C., joined in calling for a special counsel. "On too many fronts, from Iraq to environmental policy, this administration has had a problem telling the truth when it conflicts with its political agenda," he said. "I do not trust John Ashcroft to get to the bottom of this on his own."