Senate Democrats derided a young White House aide’s refusal to testify about the firing of nine U.S. attorneys after President Bush’s top political adviser, Karl Rove, didn’t show up to answer the same questions.

J. Scott Jennings, the deputy White House political director, told the Senate Judiciary Committee in Washington that he was bound by Mr. Bush’s order not to describe internal administration discussions about the dismissals. The 29-year-old aide refused even to say if he was involved in the appointment of U.S. attorneys.

“Let’s not be too contemptuous of this committee,” responded Senator Leahy, a Vermont Democrat and the panel’s chairman. “I’m just asking what kind of work you do,” he said, adding, “It sounds to me like the American taxpayers are paying you to stonewall.”

Mr. Rove, designated by White House Counsel Fred Fielding as “immune” from congressional subpoena because he is an “immediate” adviser to Mr. Bush, was a no-show at the hearing.

Senator Durbin, an Illinois Democrat, offered Mr. Jennings some sympathy for his predicament, which includes the threat of being cited for contempt of Congress.

“Where is Karl Rove?” Mr. Durbin asked. “Why is he hiding? Why does he throw a young staffer like you into the line of fire while he hides behind the White House curtains?”