The White House, however, did offer again to make former counsel Harriet Miers and one-time political director Sara Taylor available for private, off-the-record interviews.
The latest move in the separation of powers fight between the legislative and executive branches came as members of Congress began returning from their Fourth of July recess. An atmosphere of high tension accompanied the resumption of work as a fight also loomed there between majority Democrats and some key Republicans and Mr. Bush over his Iraq war policy.
In a letter to the heads of the House and Senate Judiciary panels, White House counsel Fred Fielding insisted that Mr. Bush was acting in good faith and refused lawmakers' demand that the president explain the basis for invoking the privilege.
"You may be assured that the president's assertion here comports with prior practices in similar contexts, and that it has been appropriately documented," the letter said.
Retorted House Judiciary Committee Chairman John Conyers:
"Contrary what the White House may believe, it is the Congress and the courts that will decide whether an invocation of executive privilege is valid, not the White House unilaterally," the Michigan Democrat said in a statement.
The exchange Monday was the latest step in a slow-motion legal waltz between the White House and lawmakers toward eventual contempt-of-Congress citations. If neither side yields, the matter could land in federal court.
In his letter regarding subpoenas the Judiciary panels issued, Fielding said, "The president feels compelled to assert executive privilege with respect to the testimony sought from Sara M. Taylor and Harriet E. Miers."
Fielding was responding to a 10 a.m. EDT deadline set by the Democratic chairmen, Sen. Patrick Leahy of Vermont and Rep. John Conyers of Michigan, for the White House to explain its privilege claim, prove that the president personally invoked it and provide logs of which documents were being withheld.
As expected, Fielding refused to comply. He said he was acting at Mr. Bush's direction, and he complained that the committees had decided to enforce the subpoenas whether or not the White House complied.
"The committees have already prejudged the question, regardless of the production of any privilege log," Fielding wrote. "In such circumstances, we will not be undertaking such a project, even as a further accommodation."
The privilege claim on testimony by former aides won't necessarily prevent them from appearing under oath this week, as scheduled.
Leahy said that Taylor, Mr. Bush's former political director, may testify as scheduled before the Senate panel on Wednesday. The House Judiciary Committee scheduled Miers' testimony for Thursday, but it was unclear whether she would appear, according to congressional aides speaking on condition of anonymity because negotiations were under way.
The probe into the U.S. attorney firings was only one of several Democratic-led investigations of the White House and its use of executive power spanning the war in Iraq, Mr. Bush's secretive wiretapping program and his commutation last week of I. Lewis "Scooter" Libby's prison sentence.
Fielding's letter welcomed lawmakers back to town with a clear indication that relations between Congress and the White House had soured during the break.
Mr. Bush's counsel cloaked his tough rejoinder to the Democratic committee chairmen in gentlemanly language, but his message was unequivocal: the White House won't back down, and believes the congressional legal argument to be far weaker than its own and its attitude less appealing.
Fielding dismissed the chairmen's attempt to "direct" the White House to provide the legal underpinning of Mr. Bush's executive privilege claims and a detailed listing of the documents he is withholding. He said the White House already has provided its legal argument and so does not need to do so again — and won't.
"We are aware of no authority by which a congressional committee may `direct' the Executive to undertake the task of creating and providing an extensive description of every document covered by an assertion of Executive Privilege," he wrote. Fielding suggested that asserting executive privilege on the testimony comes as a result of this impasse and the lack of good faith it demonstrates on the part of Congress.
More broadly, Fielding suggested that the congressional inquiry into the entire matter of the U.S. attorneys' dismissals has no constitutional basis, in large part because the president has sole authority to hire and fire federal prosecutors.
"Although we each speak on behalf of different branches of government, and perhaps for that reason cannot help having different perspectives on the matter, it is hoped you will agree, upon further reflection, that it is incorrect to say that the President's assertion of executive privilege was performed without `good faith,' " Fielding's letter said.
Sen. Orrin Hatch, a senior Republican on Leahy's committee, defended the White House Sunday.
"There comes a point where the White House has to say, 'Hey, look there are certain confidential things in the White House that we're not going to share with Congress, just like there are certain confidential things in Congress that we're not going to share with the White House,"' Hatch, R-Utah, said on CBS' Face the Nation.
Meanwhile, the Senate is expected to start debate this week on a bill authorizing military spending in Iraq for the fiscal year starting in October.
Perhaps most significantly, there is now debate inside the administration about whether to begin pulling out troops a lot earlier than previously expected, CBS News senior White House correspondent Bill Plante reports.
However, the administration alsoabout a report due Sunday on whether the Iraqi government is meeting political, economic and security benchmarks that Mr. Bush set in January when he announced a buildup of 21,500 U.S. combat forces.
White House press secretary Tony Snow said Monday that all of the additional troops had just gotten in place and it would be unrealistic to expect major progress now.
"You are not going to expect all the benchmarks to be met at the beginning of something," Snow said. "You are hoping that you are going to be able to see progress in terms of meeting benchmarks from that beginning stage to what you see in two months."
On Iraq, Democrats expect to resume legislative challenges to Mr. Bush's policy on the war as the Senate this week takes up a major defense spending bill. The administration has been concerned about an escalation of Iraqi war fervor. So much so that Defense Secretary Robert Gates canceled a four-nation South American tour this week to work with the White House on Iraq policy.
There have been no decisions made within the White House regarding any changes to the Iraq strategy, but the most pressing question is how to keep more Republicans from distancing themselves publicly from the Mr. Bush's policy, Plante reports.
Last week, Republican Sen. Pete Domenici of New Mexico expressed doubts about the current U.S. military tack in Iraq, joining a recent wave of fellow GOP senators that includes John Warner of Virginia, George Voinovich of Ohio and Richard Lugar of Indiana.