The Post findings paint a picture of a country at a crossroads, where long-standing privacy principles are under challenge by these new efforts to keep the nation safe.

The public face of this pivotal effort is Napolitano, the former governor of Arizona, which years ago built one of the strongest state intelligence organizations outside of New York to try to stop illegal immigration and drug importation.

Napolitano has taken her "See Something, Say Something" campaign far beyond the traffic signs that ask drivers coming into the nation's capital for "Terror Tips" and to "Report Suspicious Activity."

She recently enlisted the help of Wal-Mart, Amtrak, major sports leagues, hotel chains and metro riders. In her speeches, she compares the undertaking to the Cold War fight against communists.

"This represents a shift for our country," she told New York City police officers and firefighters on the eve of the 9/11 anniversary this fall. "In a sense, this harkens back to when we drew on the tradition of civil defense and preparedness that predated today's concerns."

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From Afghanistan to Tennessee

On a recent night in Memphis, a patrol car rolled slowly through a parking lot in a run-down section of town. The military-grade infrared camera on its hood moved robotically from left to right, snapping digital images of one license plate after another and analyzing each almost instantly.

Suddenly, a red light flashed on the car's screen along with the word "warrant."

"Got a live one! Let's do it," an officer called out.

The streets of Memphis are a world away from the streets of Kabul, yet these days, the same types of technologies and techniques are being used in both places to identify and collect information about suspected criminals and terrorists.

The examples go far beyond Memphis.

* Hand-held, wireless fingerprint scanners were carried by U.S. troops during the insurgency in Iraq to register residents of entire neighborhoods. L-1 Identity Solutions is selling the same type of equipment to police departments to check motorists' identities.

* In Arizona, the Maricopa County Sheriff's Facial Recognition Unit, using a type of equipment prevalent in war zones, records 9,000 biometric digital mug shots a month.

* U.S. Customs and Border Protection flies General Atomics' Predator drones along the Mexican and Canadian borders - the same kind of aircraft, equipped with real-time, full-motion video cameras, that has been used in wars in Kosovo, Iraq and Afghanistan to track the enemy.

The special operations units deployed overseas to kill the al-Qaeda leadership drove technological advances that are now expanding in use across the United States. On the front lines, those advances allowed the rapid fusing of biometric identification, captured computer records and cellphone numbers so troops could launch the next surprise raid.

Here at home, it's the DHS that is enamored with collecting photos, video images and other personal information about U.S. residents in the hopes of teasing out terrorists.

The DHS helped Memphis buy surveillance cameras that monitor residents near high-crime housing projects, problematic street corners, and bridges and other critical infrastructure. It helped pay for license plate readers and defrayed some of the cost of setting up Memphis's crime-analysis center. All together it has given Memphis $11 million since 2003 in homeland security grants, most of which the city has used to fight crime.