By Christine Kearney

NEW YORK, July 1 (Reuters) - Thousands of additional law enforcement officers within 50 miles (80 km) of New York City will have access to radiation detectors for dirty bombs and nuclear devices, New York police said on Wednesday.

The detectors, including cell phone-sized devices that officers wear on their belts, can help uncover a dirty bomb might be assembled outside New York and smuggled in, police said at a security conference. New York Police Department officers have used such devices for several years.

Police spokesman Paul Browne said thousands of law enforcement officers in areas surrounding New York City, including state police and sheriff's departments in New Jersey and Connecticut, were joining New York in a program aimed at detecting dirty bombs and averting nuclear attacks.

The increase in officers and equipment was being funded by a federal program called "Securing the Cities" that had been allocated $54 million in the past three years, Browne said.

Nearly eight years after the Sept. 11 attacks in 2001, New York remains the top target for groups like al Qaeda planning attacks on the United States, police and lawmakers said, and the possibility of a radiological attack on a public transport system remained high.

"We know that terrorists come here and we know that they are surveying here," said Captain Michael Riggio of the NYPD counterterrorism division.

The belt devices, which buzz when they detect radiation, are the "first line of defense" against a possible dirty bomb or a small-scale nuclear device, he said.

A dirty bomb, which combines conventional explosives such as dynamite with radioactive material, could have a devastating impact and close down the surrounding area for several years.