A former United States attorney for the District of Columbia, Joseph E. diGenova, said that by suggesting that any contempt efforts would be blocked by the Justice Department, the administration was “making it clear that this is not going to be an easy road for Congress to go and the president will use all his powers to make it difficult for them.”

Administration officials have cited a 1984 internal legal memorandum written by the Justice Department when Congress sought to charge a Reagan administration official with contempt. The memorandum concluded that a United States attorney was not required to bring a contempt charge if requested to do so by Congress. In addition, the memorandum said that contempt of Congress would not apply to an executive branch official “who asserts the president’s claim of executive privilege.”

Senator Patrick J. Leahy, Democrat of Vermont and chairman of the Judiciary Committee, said any effort by the White House to block the federal prosecutor from bringing a contempt citation on behalf of Congress would demonstrate the very problem Congress was seeking to investigate: whether federal prosecutors have been subjected to political influence.

“This administration has consistently chosen to stonewall Congressional oversight attempts, and this latest decision to interfere with those checks and balances is deeply disturbing,” Mr. Leahy said.

Underlying the discussion is the awkward procedure Congress would normally use to hold someone in contempt. Under most circumstances, Congress would have to ask the federal prosecutor in Washington to convene a grand jury and consider indicting on contempt charges any official who refused to respond to Congress’s requests for information or testimony. But the officials who have refused to cooperate — Harriet E. Miers, the former White House counsel, and Joshua B. Bolten, Mr. Bush’s chief of staff — have declined to do so because the White House has invoked executive privilege.

In addition, Sara M. Taylor, a former White House political director, refused to answer several questions when she appeared before the Senate Judiciary Committee, also citing executive privilege.

Congress has another route to enforce its will, an inherent power of contempt. But that has not been used since early in the 20th century. It has long been deemed unwieldy in the modern era as it entails Congress stopping all work to hold its own trial and imprisoning any offenders in the basement of the Capitol.