"As many as we find, we miss so many more," Alex Stone-Tharp, 21, said on a recent afternoon while combing the streets, clipboard in hand, counting cameras in the scorching heat.

A student at Sarah Lawrence, Stone-Tharp is among a dozen college interns enlisted by the New York Civil Liberties Union to bolster their side of a simmering debate over whether surveillance cameras wrongly encroach on privacy, or effectively combat crime and even terrorism — as in the London bombings investigation, when the cameras were used to identify the bombers.

The interns have spent the summer stalking Big Brother — collecting data for an upcoming NYCLU report on the proliferation of cameras trained on streets, sidewalks and other public spaces.

New York City police detectives regularly rely on private security cameras in a bid to solve crimes.

After makeshift grenades exploded outside the British consulate in midtown Manhattan on May 5, they studied scores of videotape and concluded that a still-unidentified cyclist likely tossed the devices before fleeing.

In London, British police used videotape from some of their Underground system's 6,000 cameras to help identify the suicide bombers on July 7 and the suspects in a failed attack on July 21. But as the bombings showed, the cameras do not deter determined attackers.

At last count in 1998, the New York Civil Liberties Union found 2,397 cameras used by a wide variety of private businesses and government agencies throughout Manhattan. This time, after canvassing less than a quarter of the borough, the interns so far have spotted more than 4,000.

The preliminary total "only provides a glimpse of the magnitude of the problem," said NYCLU Executive Director Donna Lieberman. "Nobody has a clue how many there really are."

But aside from sheer numbers, the NYCLU says it's concerned about the increasing use of newer, more powerful digital cameras that — unlike boxy older models — can be controlled remotely and store more images.

The group expects to eventually publicize its findings to convince the public that the cameras should be regulated to preserve privacy and guard against abuses like racial profiling and voyeurism. Privacy advocates have cited a case earlier this year in which a police videotape that captured a suicide at a Bronx housing development later turned up on a pornographic Web site.

The NYCLU plans to post an interactive map on its Web site pinpointing the location of each surveillance camera, and it may include a feature for the camera-shy that would highlight the least-surveilled route between two points.

But the map could be obsolete on arrival.

The Metropolitan Transportation Authority plans to spend up to $250 million (euro200 million) to install new surveillance cameras in the city's vast subway system. The New York Police Department also has requested funding for about 400 digital video cameras to help combat robberies and burglaries in busy commercial districts.

Police officers already watch live feeds from hundreds of cameras in city housing projects throughout the five boroughs, where "they are a proven deterrent," said NYPD spokesman Paul Browne.

Elsewhere, Chicago recently spent roughly $5 million (euro4 million) on a 2,000-camera system, which has been credited for reducing crime to its lowest point in some 40 years. In Washington, D.C., Homeland Security officials have announced plans to spend $9.8 million (euro7.8 million) for surveillance cameras and sensors on a rail line near the Capitol. And in Philadelphia, where the city has increasingly relied on video surveillance, cameras caught a murder and ultimately led to the capture of a suspect.

The NYCLU's Lieberman concedes the cameras can help solve crimes. But she claims there's no proof that they deter terrorism or more mundane crime, and some critics say it just pushes crime to where the cameras aren't.

"No one's saying there should be no video cameras, but let's not look at them as a quick fix," she said.

Whether the cameras threaten or protect society, the interns have encountered hurdles in their counting.

At one point, uniformed officers outside the Federal Reserve Bank demanded identification and warned, "if the information we had fell into the hands of terrorists, it would be a problem," said Peter Pantelis, 20, a student at the University of Pennsylvania.

Susanna Groves, 19, of the University of Michigan, recalled finding herself staring up an ornate streetlight, convinced a hidden camera was snapping pictures of her.

"I know I'm getting paranoid," she said. "But I also know there are a lot of cameras out there."