Democrats, citing a report by the nonpartisan Congressional Research Service, say presidential advisers, including 47 from the Clinton administration alone, have frequently testified before Congressional committees, both while serving the president and after they had left the White House.

Even so, legal experts say precedent does not play a role in decisions about whether to waive executive privilege; each administration, in effect, writes its own rules. The Bush administration has been particularly protective of executive privilege, and Republicans close to the White House say the decision about whether, or how much, to cooperate will come down to a calculation of the political risks and rewards.

Image Karl Rove, President Bushs chief political adviser, is among the officials who may be subpoenaed to testify publicly and under oath. Credit... Jim Bourg/Reuters

Senior White House officials have given public testimony in the past, including before the commission investigating the Sept. 11 attacks. But more times than not, it has come on the administration’s terms; Mr. Bush and Vice President Dick Cheney agreed to appear before the Sept. 11 commission, but only in private and without being required to take an oath.

When Congress and the president have not been able to resolve fights over executive privilege, it has sometimes been left to the courts to decide — most notably during the Nixon administration and the legal battle over the White House tapes. But the courts have also tried to steer clear of the wrangling over executive privilege when it is deemed strictly political.

Television talk shows on Sunday were filled with discussion of the prosecutors’ dismissals, and whether they would cost Mr. Gonzales his job. While Mr. Gonzales did not appear on any of the programs — he declined requests from at least two networks — two of the prosecutors who had been fired spoke out, as did at least five senators, including Mr. Leahy and a Republican colleague on the Judiciary Committee, Senator John Cornyn of Texas.

None of the Republicans who took to the airwaves on Sunday offered a spirited defense of the administration, but Mr. Cornyn and others did take exception to the Democratic vow to subpoena White House officials and accused some Democrats of trying to turn the issue to their political advantage.