As part of a new initiative to secure New York City from a largescale terrorist attack, the police department will employ a new technology in the subway system designed to detect the harmful radiation present in nuclear weapons, the police commissioner, Raymond Kelly, told The New York Sun in an interview.

The fresh technology, currently in its final phase of testing, will become part of the $30 million Securing the Cities Implementation initiative, a partnership between the Department of Homeland Security and local law enforcement. The goal of the program is to bar nuclear weapons from the city by creating a 50-mile protective perimeter.

The new technology would bolster the city’s nuclear exposure programs because the detectors decipher between deadly radiation in nuclear weapons and harmless radiation carried by New Yorkers involved in recent medical tests, Mr. Kelly said.

“It tells you precisely what the element is and how much radiation, which is 90% of the battle,” Mr. Kelly said.

The detectors function by differentiating between harmful and innocuous isotopes in radiation, a spokeswoman for the Domestic Nuclear Detection Office, Jenny Burke, said.

Even while the new detectors are in development, Mr. Kelly said the police department is designing a state-of-the-art sport-utility vehicle that will mobilize the fresh technology, allowing it to detect harmful weapons such as dirty bombs at bridges and tunnels.

Because New York City was selected to pilot the securing the cities initiative, it will be the first jurisdiction in America to utilize the new radiation detectors that the Department of Homeland Security plans to implement in major metropolitan areas across the country.

The new radiation detection technology is being tested at the New York Container Terminal by the DNDO. A cargo portal has been constructed to screen for ships carrying harmful nuclear materials. The pilot program, which has been given $178 million in funding from the Department of Homeland Security, is not only part of the agency’s goal of screening 98% of all containers entering America, but also the nuts and bolts for the burgeoning technology that will strengthen the city’s defenses against large-scale nuclear attacks.

“The biggest benefit to me is the emitter identification,” Mr. Kelly said. “It’s going to come in a lot of different sizes and shapes.”

While specialized units in the force presently use sophisticated radiation detectors and about 700 supervisors carry hand-held devices, the new technology will allow the department to cast a wider net.

“Something we really have to worry about is false positives,” Mr. Kelly said. “You can have these detectors in the subway, and it will be geared toward vehicles.”

The Department of Homeland Security, which has been criticized in the past for setting its own agenda on counter-terrorism efforts, has made a point of coordinating the planning of the initiative with state and local authorities.

The city’s police department, which Mr. Kelly called a “conduit” of the initiative, has organized several meetings between local law enforcement departments and federal agencies to plan steps going ahead.

A staff inspector with the New York State police who has worked closely with the initiative, David McBath, said New York City has led the effort in coordinating the “cutting edge” program.

The city’s police department has set up three subcommittees of law enforcement officials to analyze equipment, concept of operations, and training and exercise, Mr. McBath said.

“It’s all about intelligence policing,” Mr. McBath said. “This is a new role in law enforcement.”

Catalyzed by resurging terrorist networks and a growing market for materials used in the production of nuclear weapon worldwide, radiation detection technology is a necessity for New York City, a senior fellow and policy analyst at the Manhattan Institute, R.P. Eddy said. He points to a recently released study on the vulnerability of urban populations to nuclear attacks conducted by the International Journal Health Geographics. The study paints a morbid picture of how New York would be able to cope with a nuclear attack.

“Obviously this is worse than we thought it would be,” Mr. Eddy said. “Preventing nuclear attacks should be the no. 1 tactical issue.”