Defense Secretary Donald H. Rumsfeld (search) warned on Wednesday that terrorists are regrouping for another strike, but the United States is preparing to deal with any threat.

"The extremists continue to plot to attack again. They are at this moment recalibrating and reorganizing. And so are we," the Pentagon chief told members of the House Armed Services Committee in prepared testimony.

Offering his argument for President Bush's request for $419 billion in defense spending for fiscal 2006, Rumsfeld said the plan sets an ambitious course to "continue prosecuting the war and to attack its ideological underpinnings."

In the first of back-to-back testimony, the defense secretary said the times ahead will be challenging and focused on two central realities of the War on Terror (search). He said the fight to defeat terrorism can't be won by military means alone and that other agencies must be involved as well. Rumsfeld said, "The United States cannot win a global struggle alone."

"It will take cooperation among a great many nations to stop weapons proliferation (search)," he said. "It will take a great many nations working together to locate and dismantle global extremist cells. It takes a great many nations to gather and share the intelligence crucial to stopping future attacks."

Rumsfeld spoke to lawmakers increasingly concerned about an exit strategy for Iraq, a timetable for troops to return home and the skyrocketing costs of the war. Earlier this week, President Bush asked Congress for $82 billion in emergency money to fund the Iraq and Afghanistan wars.

"The future of this conflict is not predictable. So additional funds will have to be requested as required," Rumsfeld said Wednesday.