Cops patrolling Times Square on New Year's Eve will be armed with high-tech sensors to protect revelers against the possibility of nuclear terrorism, The Post has learned.

A "substantial number" of lawmen on duty will be using "personal radiation detectors" on loan from the U.S. Customs Service. 

The device, which is slightly larger than a pack of cigarettes, is capable of alerting the user to radioactivity nearby, providing greater protection for the expected 1 million New Year's Eve revelers who will watch the ball drop in Times Square. 

Inspector Christopher Rising, an NYPD spokesman, declined to say how many members of the force would be provided with the gadgets, which are triggered by extremely low levels of gamma rays and X-rays. 

"Our responsibility is to keep everyone safe. New York City post-Sept. 11, as well as the rest of the country, posts new challenges, and the NYPD is continuing to do everything it can to keep New York City the safest large city in America," said Rising. 

The black gadget, which weighs 6 ounces, measures 4.1 inches high, 2.4 inches wide and 0.9 inches thick, and is carried in a Velcro belt holster. It is powered by two AA alkaline batteries and costs $1,400. 

If it detects radiation, the device vibrates, sounds a tone and displays flashing yellow lights. 

Rising said the plan to use the device in Times Square is strictly "precautionary" and not based on a specific threat. 

"Customs has been using them for a while to test shipments. They're not designed to give a pinpoint reading - they're designed to tell you where you're safe to be," he explained. 

A spokesman for Sensor Technology Engineering Inc., of Santa Barbara, Calif., the company that makes the tool, would not provide basic production information, insisting it was designed solely for "governments, countries, municipalities and security concerns." 

"If you're not one of those, you have no purpose purchasing it," said he spokesman, who declined to give his name. "It's a very, very sensitive device. 

"If they come into anything that emits radiation, it will sound an alarm and tell someone they need to investigate further." 

Sources said the NYPD has used the device before, although details were not immediately available. 

It also has proved effective elsewhere in the war against terrorism. 

John A. Gordon, undersecretary of the U.S. Department of Energy, told the Senate Appropriations Committee on May 9 that a year earlier, Uzbekistan customs officers using a similar detector seized 10 containers of highly radioactive material that were suspected of being intended for use in a "radiation-dispersal bomb." 

U.S. Customs spokesman James Michie had no details about that incident, but said his agency had "trained border guards from approximately 20 countries on how to look for radioactive materials that could possibly be used to construct weapons of mass destruction, and these countries include some of the former Soviet Republic."