For personal reasons, Clarke is leaving the position of assistant secretary for public affairs, the department said in a press release. She has held the job for two years, arriving the summer before the Sept. 11, 2001, terrorist attacks on the Pentagon and World Trade Center.
"I depart sadly because this has been the best professional experience of my life," she said in a press release. "It has been a true honor working for the men and women of the U.S. military."
Clarke was a regular fixture at Pentagon briefings during military operations in Iraq.
Lawrence DiRita, special assistant to Defense Secretary Donald H. Rumsfeld, will do her job until a permanent replacement is confirmed.
In the press release, Rumsfeld called Clarke "a gifted communicator," praising her office for its efforts "to tell the story of our fighting force and bring their courage, dedication and professionalism into sharp focus for all Americans."
President Bush's press secretary, Ari Fleischer, talked about Clarke's resignation with reporters aboard Air Force One. "Tori is great. Tori is wonderful at what she does," Fleischer said, using her nickname. "She's served our country very well."