NEW YORK - (AP) - In a city considered the nation's No. 1 terrortarget, few sites worry police more than the New York City subways- a sprawling, 24-hour-a-day system with 5 million riders.

The NYPD has been vigilant about defending the subways againstterror since the recent bombing in Moscow, and the plea earlierthis year of Najibullah Zazi toplotting a suicide bomb attack on Manhattan subways.

Officials have used bomb-sniffing dogs, security cameras andhigh-tech explosive detection devices to defend against possibleterror attacks.

And they also use beat cops to man lonely posts at the mouths ofsubway tunnels that run beneath the East River. One of the exits isbehind a phony town house on a cobblestoned block in Brooklyn.