President Bush yesterday defended the White House strategy for preventing future terrorist attacks and warned that the London bombings were part of a broader campaign to scare the United States and its allies into retreat.

"These attacks were barbaric, and they provide a clear window into the evil we face," Bush said in a speech at the FBI Academy, at the Marine base in Quantico. "The aim of the terrorists is to remake the Middle East in their own grim image of tyranny and oppression by toppling governments, by exporting terror, by forcing free nations to retreat and withdraw."

Although U.S. and British officials do not know who carried out the London subway bombings that killed 52 people and wounded more than 700, Bush said it is imperative that the United States and its allies wage an offensive war to hunt down terrorists before they strike again. "These kind of people who blow up subways and buses are not people you can negotiate with, or reason with, or appease," Bush said. The president said the U.S. military operation in Iraq is central to defeating these terrorists: "The terrorists fight in Iraq because they know that the survival of their hateful, hateful ideology is at stake."

Democrats, however, say the Iraq war has diverted U.S. attention and resources away from securing ports, airports and other potential terrorist targets and left Osama bin Laden, the mastermind of the Sept. 11, 2001, attacks, on the loose.

"We should take very seriously the lesson learned from the attacks in London: Fighting terrorism overseas is not enough to ensure that terrorists will not strike American soil again," Senate Minority Leader Harry M. Reid (D-Nev.) said in a statement. "We spend more in Iraq in a single month than we spend on first responders all year. Failure in Iraq is not an option, and we will continue to support our troops but we must do more to support the war on terror here at home."

As part of the broader effort to defend the administration's approach, Bush told an audience of Marines, FBI recruits and first responders that the White House has tripled homeland security spending since 2001. "In an age of new dangers, we're doing everything in our power to do our jobs," Bush said. But, repeating a line other White House officials have been using since the bombings, he said, "We know that there is no such thing as perfect security, and that in a free and open society it is impossible to protect against every threat."

Bush, who has strong public support for his anti-terrorism policies even as his overall popularity sags, used his first speech since the London bombings to lobby Congress to endorse his agenda, including extending the USA Patriot Act, which provides federal and state authorities greater power to hunt down potential terrorists. Critics from both parties have said the act jeopardizes the civil rights of ordinary citizens.

Still, the central -- and most contentious -- focus of the Bush strategy is Iraq. With public support for the military operation slipping, Bush said the London bombings, much like the suicide attacks carried out by insurgents in Iraq, are designed to pressure the United States and its allies to surrender. "The terrorists know they can't defeat us on the battlefield," Bush said. "The only way the terrorists can win is if we lose our nerve. This isn't going to happen on my watch."

Bush, who was with British Prime Minister Tony Blair in Scotland during last week's attacks, said the United States is assisting the Blair government in trying to find those who carried out the subway bombings and to share intelligence on future terrorism.

"The city that survived the Nazi blitz will not yield in the face of thugs and assassins. And just as America and Great Britain stood together to defeat the totalitarian ideologies of the 20th century, we now stand together against the murderous ideologies of the 21st century," Bush said.