The revelation came as a federal prosecutor continues to investigate the leaking of the identity of a CIA agent, Valerie Plame, in 2003 after her diplomat husband criticized the Bush administration's rationale for the war.
In this 03 November, 2005, file photo, former Chief of Staff for US Vice President Dick Cheney, I. Lewis Scooter Libby (C-on crutches) is surrounded by the media as he walks out of US District Court in Washington, DC with his attorney Ted Wells (L).
Libby, who is currently facing charges of obstruction and lying in the investigation, is suspected of having revealed Plame's job as an undercover CIA agent to a reporter -- a federal crime in the United States.
According to a document filed Wednesday by federal prosecutor Patrick Fitzgerald, Libby said he spoke to a New York Times reporter in July 2003 after learning from Vice President Dick Cheney that Bush had authorized intelligence leaks.
"Defendant's participation in a critical conversation with Judith Miller ... occurred only after the vice president advised defendant that the president specifically had authorized defendant to disclose certain information in the NIE" (National Intelligence Estimate)," the document said.
The court document does not indicate that Bush or Cheney told Libby to unveil Plame amid the ongoing intrigue over the US drive to war with Iraq in 2003.
But Libby will go on trial in January 2007 on charges of obstruction of justice, perjury and making false statements related to the Plame affair to investigators. Libby denies the charges.
The case arose from a probe into the outing of Central Intelligence Agency spy Plame, who was exposed, Bush critics allege, by senior officials angry that her husband ambassador Joseph Wilson had criticised the drive to war with Iraq.
In mid-2003, after the US had invaded Iraq, Wilson in a newspaper piece publicly challenged the Bush administration's pre-war assertion that Saddam Hussein had sought to buy uranium from Niger for weapons use.
The assertion had been one of the key justifications for the war.
Weeks after the Wilson article, Plame's identity was revealed in a newspaper opinion column which sought to discredit Wilson's argument.
After the leak, the CIA maintained that Plame's value as a secret agent was irrevocably damaged.
The White House had no comment Wednesday on the new revelation, but opposition politicians pounced on it.
Senate Democratic leader Harry Reid cited Bush's repeated denials of any knowledge of secret information leaks.
"I don't know of anybody in my administration who leaked classified information. If somebody did leak classified information, I'd like to know it, and we'll take the appropriate action," the president had said in September 2003.
"In light of today's shocking revelation, President Bush must fully disclose his participation in the selective leaking of classified information," Reid said. "The American people must know the truth."
The CIA leak scandal was one of a string of dramas last year that helped dent Bush's opinion poll ratings, and still hangs over the White House.
Bush's political guru Karl Rove was not indicted along with Libby last year, but has been told he is still under investigation.
Libby resigned from his post as Cheney's chief of staff when he was indicted.