WASHINGTON, USA (AP) – Lawyers for US Vice-President Dick Cheney’s former top aide are signalling they may delve deeply at his criminal trial into infighting among the White House, the CIA and the State Department over pre-Iraq war intelligence failures.

In a prelude to a possible defence, the lawyers for I Lewis “Scooter” Libby also are suggesting that the State Department – not Libby – may be to blame for leaking the identity of covert CIA officer Valerie Plame to the media.

Court papers filed late Friday raise the possibility a trial could become politically embarrassing for the Bush administration by focusing on the debate about whether the White House manipulated intelligence to justify the US-led invasion of Iraq in March 2003.

The defence team stated that in June and July 2003, Plame’s CIA status was at most a peripheral issue to “the finger-pointing that went on within the executive branch about who was to blame” for the failure to find weapons of mass destruction in Iraq.

“If the jury learns this background information” about finger-pointing “and also understands Mr Libby’s additional focus on urgent national security matters, the jury will more easily appreciate how Mr Libby may have forgotten or misremembered … snippets of conversation” about Plame’s CIA status, the lawyers said.

Cheney’s former chief of staff was indicted October 28 on five counts of perjury, obstruction and lying to the FBI about how he learned of Plame’s CIA employment and what he told reporters about her.

Three key prosecution witnesses are NBC correspondent Tim Russert, former New York Times reporter Judith Miller and Time magazine reporter Matt Cooper.

Libby’s lawyers are asking US District Judge Reggie Walton for access to government documents about a 2002 trip that Plame’s husband, former Ambassador Joseph Wilson, made to the African nation of Niger at the CIA’s behest and about “his wife’s involvement” with that mission.

The documents relate to what prospective witnesses – including then-Deputy Secretary of State Richard Armitage and deputy White House chief of staff Karl Rove – probably would say at Libby’s trial.

Noting press reports last week, the court papers say there has been speculation that Armitage told The Washington Post’s Bob Woodward that Wilson’s wife worked at the CIA, and speculation that Woodward’s source and the primary source for conservative columnist Robert Novak are the same person.

Novak disclosed Plame’s identity on July 14, 2003, eight days after Wilson contended in a New York Times op-ed column that the administration was twisting pre-war intelligence to exaggerate the Iraqi threat from a nuclear weapons programme.

“If the facts ultimately show that Mr Armitage or someone else from the State Department was also Mr Novak’s primary source, then the State Department and certainly not Mr Libby bears responsibility for the ‘leak’ that led to the public disclosure” of Plame’s CIA identity, Libby’s lawyers said.

Rove – a source for Novak and Cooper – is under investigation by Special Counsel Patrick Fitzgerald in the probe of the leak of Plame’s CIA identity.

In a conversation that Rove says he forgot about until a year after the investigation began, Rove spoke to Cooper about the CIA connection of Wilson’s wife. Cooper subsequently wrote a story headlined, “A War On Wilson?”

Libby’s lawyers say that “either the government or the defence may call Mr Rove as a witness at trial” and note that “the grand jury’s investigation may be continuing with respect to Mr Rove or other witnesses”.

The defence says the documents it seeks will help demonstrate that the White House did not launch a concerted effort to punish Wilson by leaking his wife’s identity, as administration critics have alleged.