President Bush said that U.S. troops have hard work in Iraq, but their mission there will not change because of a recent upsurge（高潮）in fighting.

"There is nothing they can do to intimidate（胁迫）us, to make us change our deepest belief," he said. "They are trying to kill to shake our will. We are too tough, too strong, too resolute and too determined to ever have our will shaken by thugs（暴徒）and terrorists."

Mr. Bush was in New York campaigning for the extension of a controversial anti-terrorism law, which removes barriers to sharing information between U.S. law enforcement and intelligence agencies. It also makes it easier to conduct electronic surveillance（监视）and wiretaps（窃听）on suspected terrorists.

Concerns about the potential abuse of those broader policing powers have made the so-called Patriot Act a campaign issue. The presumptive Democratic challenger, Massachusetts Senator John Kerry, voted for the act, but has since expressed concerns about its implementation.

Mr. Bush said that the law has made the nation safer at a time when America is also confronting threats abroad.

"As we work to not only make the homeland more secure, we work to spread freedom which will make the world more peaceful," he added. "The enemy can't stand the thought of free societies. That's why they attacked us."

The president's handling of the war in Iraq is a central issue in this year's campaign. The latest public opinion polls show Mr. Bush leading Senator Kerry 48 percent to 44 percent.

A Washington Post/ABC television poll shows that a majority of Americans still believe that invading Iraq was the right thing to do. Nearly two-thirds said that U.S. operations there have bogged down and are not making good progress, but an even greater number favor sticking with a June 30 deadline for handing over political power to a transitional government until elections can be held.