Defense Secretary Donald H. Rumsfeld said he essentially was too busy to testify at a public hearing on the Iraq war, raising a new furor on Capitol Hill over the three-year-old conflict.

Speaking to Pentagon reporters Wednesday, Rumsfeld said he thought it was enough for him to attend a private briefing with the entire Senate on Thursday. Citing his crowded calendar, he declined the Senate Armed Services Committee's request to testify publicly on Thursday morning.

Rumsfeld suggested that complaints about his decision could be politically motivated.

"Let's be honest: Politics enters into these things, and maybe the person raising the question is interested in that," said Rumsfeld, without identifying anyone. The defense secretary said he had testified in the past and was not reluctant to face off against some of the committee's more vocal war critics, including Sen. Edward M. Kennedy, D-Mass.

Rumsfeld's decision drew protests from committee Democrats who said much had changed in the six months since he last testified and took questions from the committee. The request for his appearance came from the committee chairman, Sen. John Warner, R-Va., and the top Democrat, Sen. Carl Levin of Michigan.

"America is in deep trouble in Iraq, yet Secretary Rumsfeld refuses to explain and defend his policies in full public view tomorrow," Kennedy said.

"Avoiding a congressional hearing may take the sting out of the process for Secretary Rumsfeld, but it does nothing to reassure the American people or our men and women in uniform that we have a viable policy in Iraq," he said.

Sen. Hillary Clinton, D-N.Y., wrote Rumsfeld on Wednesday, urging him to change his mind.

"The American people should hear directly from you," said Clinton, who has criticized the administration's handling of the war. Unlike Kennedy, she has not called for Rumsfeld's resignation.

Gen. Peter Pace, chairman of the Joint Chiefs of Staff, and Gen. John Abizaid, chief of U.S. Central Command, were to testify.

Rumsfeld last appeared before the committee on Feb. 7, when he and Pace were questioned about the war's strain on the military.

In the six months since, the number of U.S. troops in Iraq has dipped but now is back up to about 133,000, as part of an effort to quell the violence in Baghdad. The total could exceed 135,000 in the weeks and months ahead.