America has made progress in the War on Terror, but the threat today may be greater than ever before because the available weapons are far more dangerous, Defense Secretary Donald H. Rumsfeld said Thursday.

"The enemy — while weakened and under pressure — is still capable of global reach, and still possesses the determination to kill more Americans — and to do so with the world's most dangerous weapons," Rumsfeld said in remarks prepared for delivery at the National Press Club.

The U.S. strategy, he said, includes doing everything possible to prevent the enemy from gaining weapons of mass destruction, improving homeland defense and intelligence gathering and helping friendly nations become better able to fight the terrorists in their own countries.

"Because they lurk in shadows, without visible armies, and are willing to wait long periods between attacks, there is a tendency to underestimate the threat they pose," said Rumsfeld. He said there are no fewer than 18 organizations, loosely connected with Al Qaeda, conducting terrorist attacks.

His remarks come as the Pentagon is preparing to release a broad four-year defense review that doesn't eliminate any major weapons programs, but calls for more spending on special operations forces, cuts in Air Force personnel, and a restructuring of the Army and reserve forces.

Rumsfeld's speech also touched on the idea that Americans must be braced for a long war on terror, a theme that both Rumsfeld and President Bush have pressed in recent days. And Rumsfeld repeated the often-stated warning that the only way terrorists win is if the U.S. loses its will to continue the fight in Iraq.

The administration has faced a growing public uneasiness with the Iraq war, which is costing more than $4 billion a month and has left more than 2,240 service members dead. Military officials have said that U.S. forces will pull out of Iraq as the Iraqi forces become more able to take over their country's security.

The Pentagon hopes to drop the total number of troops in Iraq to below 100,000 before the end of 2006, but officials say any reductions will be based on the conditions there. Currently there are about 138,000 troops in Iraq, which was the base level for much of last year before additional forces were sent in to provide security for the elections.