NEW YORK - On a cloudless spring day, the NYPD helicopter soars over the city, its sights set on the Statue of Liberty.

A dramatic close-up of Lady Liberty's frozen gaze fills one of three flat-screen computer screens mounted on a console. The hundreds of sightseers clustered below are oblivious to the fact that a helicopter is peering down on them from a mile and a half away.

“They don't even know we're here,” says crew chief John Diaz, speaking into a headset over the dim of aircraft's motor.

The unmarked helicopter's corporate, silver-and-white motif belies what's inside: an arsenal of sophisticated surveillance and tracking equipment powerful enough to stealthily read license plates - or even pedestrian's faces - from high above.

Police officials say the chopper's sweeps of the city landmarks and other potential targets are invaluable to the NYPD's post-Sept. 11 mission of guarding against another attack. They also argue that keeping it an “unmarked ship” provides a see-but-not-be-seen advantage against lurking terrorists and ordinary bad guys alike.

“It looks like just another helicopter in the sky,” said Assistant Chief Charles Kammerdener, who oversees the aviation unit.

Police Commissioner Raymond Kelly has said that “no other law enforcement agency in the country has anything that comes close” to the surveillance chopper, designed by a team of engineers at Bell Helicopter and computer technicians based on the exact specifications of the NYPD.

The helicopter is named simply “23” - for the number of police officers killed in the Sept. 11, 2001 terror attacks.

The decision to customize the helicopter at a cost of about $10 million reflects a new frontier in cutting-edge counterterrorism technology at the nation's largest police department.

Elsewhere, the NYPD plans to spend tens of millions of dollars to strengthen security in the lower Manhattan business district with a network of closed-circuit television cameras and license-plate readers posted at bridges, tunnels and other entry points. It also has deployed hundreds of radiation detectors - some worn on belts like pagers, others mounted on cars and in helicopters to detect possible dirty bombs.

Kelly even envisions someday using futuristic “stationary airborne devices” similar to blimps to conduct reconnaissance and help detect chemical, biological and radiological threats.

Civil rights advocates aren't as enthused about the push for more surveillance, arguing it reflects the NYPD's evolution into ad hoc spy agency.

“From a privacy perspective, there's always a concern that ‘New York's Finest' are spending millions of dollars to engage in peeping Tom activities,” said Donna Lieberman, executive director of the New York Civil Liberties Union.

Police insist that law-abiding New Yorkers have nothing to fear.

“Obviously, we're not looking into apartments,” Detective Diaz said during a recent flight. “We don't invade the privacy of individuals. We only want to observe anything that's going on in public.”

The helicopter's powers of observation reach far and wide, thanks largely to a robotic, high-powered camera mounted on a turret projecting from its nose like a periscope. The camera has infrared night-vision capabilities and a satellite navigation system that allows police to automatically zoom in on a location by typing in the address on a computer keyboard.

The surveillance system can beam live footage to police command centers or even to wireless hand-held devices.

“The commander on the ground can see what we're seeing,” Diaz said.

During this sweep, the helicopter circumvented Manhattan, using the camera to look for signs of trouble. The decks of Staten Island ferry terminal, the stanchions of the Verrazzano-Narrows Bridge, the giant air vents feeding the Lincoln Tunnel, the aviation fuel lines stretching toward John F. Kennedy International Airport - targeted in a plot uncovered last year - all passed inspection. Without leaving Manhattan airspace, the chopper also was able to get a crystal-clear picture of jetliners waiting to take off from LaGuardia Airport.

The aircraft has helped track down fleeing suspects, including a recent case of a gunman who had shot his wife in Queens. As officers on the ground worried about how to approach the suspect's car, the camera in the sky hovered overhead, peaked inside the vehicle and found that he had already shot and killed himself.

During the recent visit of Pope Benedict XVI, 23 patrolled the skies, at one point receiving a call from officers who had looked up and spotted a suspicious man with a camera on a Fifth Avenue rooftop near the pontiff's residence. Diaz radioed back that it was a false alarm.

“There was a modeling shoot going on,” he said.

AP-ES-05-23-08 1554EDT