WASHINGTON, April 6 — Vice President Dick Cheney's former chief of staff testified that he was authorized by President Bush, through Mr. Cheney, in July 2003 to disclose key parts of what until then was a classified prewar intelligence estimate on Iraq, according to a new court filing.

The testimony by the former official, I. Lewis Libby Jr., cited in a court filing by the government made late Wednesday, provides an indication that Mr. Bush, who has long criticized leaks of secret information as a threat to national security, may have played a direct role in authorizing disclosure of the intelligence report on Iraq.

The disclosure occurred at a moment when the White House was trying to defend itself against accusations that it had inflated the case against Saddam Hussein.

The president has the authority to declassify information, and Mr. Libby indicated in his testimony that he believed Mr. Bush's instructions — which prosecutors said Mr. Libby regarded as "unique in his recollection" — gave him legal cover to talk with a reporter about the intelligence.

Among the key judgments in the report, called a National Intelligence Estimate, was that Saddam Hussein was probably seeking fuel for nuclear weapons.

Mr. Libby did not assert in his testimony to a grand jury, first reported on the Web site of The New York Sun, that Mr. Bush or Mr. Cheney had authorized him to reveal the name of an undercover C.I.A. officer, Valerie Wilson. Mr. Libby is scheduled to go on trial next year on perjury and obstruction charges connected to the disclosure of Ms. Wilson's name.

The White House refused to discuss Mr. Libby's account, or say whether it differed with Mr. Bush or Mr. Cheney's recollections of events, which the two men described in interviews with prosecutors. "We're not commenting on an ongoing legal proceeding," said Scott McClellan, Mr. Bush's press secretary.

Democrats seized on the disclosure, and demanded that Mr. Bush — who has said he was determined to get to the bottom of the leak case — now address his role.

"In light of today's shocking revelation, President Bush must fully disclose his participation in the selective leaking of classified information," said the Democratic leader, Senator Harry Reid of Nevada. Representative Jane Harman of California, the senior Democrat on the House Intelligence Committee, said, "If the disclosure is true, it's breathtaking. The president is revealed as the leaker in chief."

Mr. Libby discussed some of the conclusions of the intelligence report with Judith Miller, then a reporter for The New York Times, in a meeting on July 8, 2003, the court documents say. The previous day, the White House, for the first time, had publicly admitted that Mr. Bush's statement in the State of the Union address earlier that year, alleging that Mr. Hussein had sought uranium in Africa, should not have been in the speech.

A little more than a week later, under continuing pressure, the White House published a declassified version of the executive summary of the estimate, in an effort to make the case that Mr. Bush's statement had been justified by the intelligence community's best judgment.

The disclosure on Wednesday night was part of the legal maneuvering over documents Mr. Libby has sought from the government to make his defense. But the political impact of the disclosure could be more significant than the legal impact.

The court filing said Mr. Libby testified that the "vice president advised defendant that the president had authorized defendant to disclose certain information in the N.I.E." The prosecutors said Mr. Libby testified that he recalled "getting approval from the president through the vice president to discuss material that would be classified but for that approval" and that those events "were unique in his recollection."

The leak was intended, the court papers suggested, as a rebuttal to an Op-Ed article in The New York Times on July 6, 2003, by Joseph C. Wilson IV, a former United States ambassador and the husband of Ms. Wilson. Mr. Wilson wrote that he traveled to Africa in 2002 after Mr. Cheney raised questions about possible nuclear purchases by Iraq. Mr. Wilson wrote that he concluded it was "highly doubtful" Iraq had sought nuclear fuel from Niger.

At Mr. Cheney's office, the Op-Ed article was viewed "as a direct attack on the credibility of the vice president (and the president) on a matter of signal importance: the rationale for the war in Iraq," according to the court papers filed by the prosecutor, Patrick J. Fitzgerald.

The filing was intended to limit the number of documents that the government has to turn over to Mr. Libby and his defense team.

By Mr. Libby's account to the grand jury, the presidential authorization to disclose selective parts of the intelligence estimate was made in advance of a meeting on July 8 between Mr. Libby and Ms. Miller. Mr. Libby brought a brief abstract of the N.I.E.'s key judgments to the meeting.

Mr. Libby testified, the prosecutors said, that he was "specifically authorized in advance of the meeting to disclose the key judgments of the classified N.I.E. to Miller on that occasion because it was thought that the N.I.E. was 'pretty definitive' against what Ambassador Wilson had said and that the vice president thought that it was 'very important' for the key judgments of the N.I.E. to come out."

The court filing said that Mr. Libby testified that he was supposed to tell Ms. Miller, among other things, that "a key judgment of the N.I.E. held that Iraq was 'vigorously trying to procure' uranium." Mr. Libby, the prosecutors, said, testified that the meeting with Ms. Miller was the "only time he recalled in his government experience when he disclosed a document to a reporter that was effectively declassified by virtue of the president's authorization that it be disclosed."

Ms. Miller did not write about the conversation before the executive summary of the document was released by the White House 10 days later.

Mr. Libby testified that he was unsure of his authority to reveal the information before he met Ms. Miller, so he spoke with David Addington, then a lawyer for Mr. Cheney whom Mr. Libby regarded as an expert on national security law.

"Mr. Addington opined that presidential authorization to publicly disclose a document amounted to declassification of the document," the filing by Mr. Fitzgerald said.

Mr. Libby testified that at the meeting he did not discuss Ms. Wilson, the C.I.A. officer at the center of the leak inquiry, because "he had forgotten by that time that he learned about Ms. Wilson's C.I.A. employment a month earlier from the vice president."

Ms. Miller wrote an account of her meeting with Mr. Libby, which was published in the Times on Oct. 16, 2005. She wrote that her notes showed that the two had discussed Mr. Wilson's wife, who according to her notes worked in a unit of the C.I.A. engaged in the assessments of unconventional weapons.

Ms. Miller said that Mr. Libby also discussed a chronology that he portrayed as "credible evidence" of Iraq's efforts to acquire uranium. She made no reference to whether Mr. Libby referred to any material as derived from the intelligence estimate, but said that he talked about two reports, one in 1999 and another in 2002, that seemed to support the contention that Iraq was interested in obtaining uranium.

Ms. Miller did not respond to telephone messages on Thursday. In the course of trying to limit Mr. Libby's demands for documents, Mr. Fitzgerald disclosed other elements of the case, and of his intentions.

He told the court that he did not intend to call to the witness stand three significant players in the leak investigation into the leak and the intelligence dispute over Niger. They are George J. Tenet, the former director of central intelligence; Stephen J. Hadley, then the deputy national security adviser and now Mr. Bush's national security adviser, and Karl Rove, the president's chief political strategist.

Mr. Rove also spoke to reporters about the intelligence dispute about Niger, and he testified repeatedly before the grand jury. He has not been charged and his lawyer has said he will be exonerated.