WASHINGTON — House Democrats on Thursday took the first step toward holding former White House counsel Harriet Miers in contempt of Congress after she defied a subpoena — at President Bush’s order — and skipped a hearing on the firing of U.S. attorneys.

Over the strenuous objections of Republicans, a subcommittee cleared the way for contempt proceedings by voting 7-5 to reject Mr. Bush’s claim of executive privilege. He says his top advisers, whether current or former, cannot be summoned by Congress.

“Those claims are not legally valid,” Rep. Linda Sanchez, Democrat of California, said of Mr. Bush’s declaration. “Ms. Miers is required pursuant to the subpoena to be here now.”

In the emotional debate that followed, Republicans complained that Democrats were choosing showy, televised proceedings and the threat of court action to force the testimony rather than agree to Mr. Bush’s offer for private, off-the-record interviews.

The White House showed no sign of giving in.

“If the House Judiciary Committee wants to avoid confrontation, it should withdraw its subpoenas,” a White House spokesman, Tony Fratto, said. “The committee is rejecting accommodation because they prefer just the kind of political spectacle they’re engaged in now.”

Ms. Miers’ testimony emerged as the battleground for a broader scuffle between the White House and Congress over the limits of executive privilege. Presidents since the nation’s founding have sought to protect from the prying eyes of Congress the advice given them by advisers, while Congress has argued that it is charged by the Constitution with conducting oversight of the executive branch.

Mr. Bush’s invocation of executive privilege comes during the Democrats’ probe of whether the firings were really an effort by the White House to fire and replace federal prosecutors in ways that might help Republican candidates. Democrats say testimony by numerous aides that Mr. Bush was not involved in deciding whom to fire undercuts his privilege claim.

Administration officials acknowledge that the firings were botched in their execution, but they insist there was no improper motive for them. They point out that U.S. attorneys are political appointees and that the president can fire them for almost any reason.

The probe has prompted calls by Democrats and a few Republicans for the resignation of Attorney General Alberto Gonzales. With Mr. Bush’s support behind him, Mr. Gonzales shows no sign of stepping down.

The dispute extended to Congress’ request for information on other matters, including the FBI’s abuses of civil liberties under the USA Patriot Act and Mr. Bush’s secretive wiretapping program.

But it is a pair of congressional subpoenas for two women who once were Mr. Bush’s top aides that has moved the disagreement to the brink of legal sanctions and perhaps a court battle.

A former White House political director, Sara Taylor, appeared Wednesday before the Senate Judiciary Committee and in a tentative performance sought to answer some lawmakers’ questions and remain mum on others, citing Mr. Bush’s claim of privilege. Senators didn’t seem eager to cite her with contempt, but Chairman Patrick Leahy, Democrat of Vermont, said he had not yet made that decision.

Ms. Miers, in contrast, chose to skip the House hearing Thursday, citing White House Counsel Fred Fielding’s letter to her lawyer conveying Mr. Bush’s order not to show up. In letters sent the night before to Judiciary Committee Chairman John Conyers and Ms. Sanchez, Messrs. Bush and Fielding cited several legal opinions that they said indicated that the president’s immediate advisers are “absolutely immune” from congressional subpoenas.

Incensed, Democrats held the hearing anyway. Addressing an empty chair at the witness table with a nameplate reading “Ms. Miers,” Ms. Sanchez and Mr. Conyers left little doubt that contempt proceedings by the full Judiciary Committee — and later the full House — would be the next step unless Ms. Miers and the administration change their positions.

“If we do not enforce this subpoena, no one will ever have to come before the Judiciary Committee again,” Mr. Conyers, Democrat of Michigan, said.

“What we’ve got here is an empty chair. I mean, that is as contemptuous as anybody can be of the government,” Rep. Steve Cohen, Democrat of Tennessee, said. “I resent the fact that this lady is not here.”

Republicans accused Democrats of proceeding in the absence of evidence of wrongdoing by Ms. Miers or any White House officials.

Rep. Chris Cannon of Utah, the ranking Republican on Ms. Sanchez’s subcommittee on commercial and administrative law, warned Democrats that a contempt citation would fail evidentiary standards in court.

“You can’t go to the courts essentially and say, ‘We don’t know what we don’t know, therefore give us a subpoena so we can find out,'” Mr. Cannon said.

“There is no proof whatsoever that Harriet Miers likely holds some smoking gun with respect to the U.S. attorney situation,” Rep. Ric Keller, Republican of Florida, said.

Several aides close to the proceedings said House Democrats were considering launching contempt proceedings against Ms. Miers in the absence of any negotiated agreement over the next few weeks.

The citation would first be debated and voted upon by the full Judiciary Committee. If approved, it then would go to the full House where it would be debated and require a majority for approval.

The House speaker, Nancy Pelosi, Democrat of California, would then refer the matter to the U.S. attorney for the District of Columbia, “whose duty it shall be to bring the matter before the grand jury for its action,” according to the law. The man who holds that job is a Bush appointee, Jeff Taylor.

Legal scholars said the issue of Ms. Miers’ immunity is far from clear-cut. No president has gone as far as mounting a court fight to keep his aides from testifying on Capitol Hill.