Also, there will be increased police activity at both terminals of the Staten Island Ferry.
More on Thursday's drill from the Associated Press writer Tom Hays:
On a cold afternoon at the mouth of New York Harbor, a tiny yellow fishing boat bobs in the water as a flotilla of law enforcement vessels fitted with sophisticated radiation detection equipment closes in.
The boat has drawn suspicion by emitting gamma rays - a sign it may be carrying a dirty bomb, packed with radioactive material.
High-speed vessels from the New York Police Department and state Naval Militia halt the boat, tie it up and accomplish their mission of neutralizing an apparent terror threat.
The radiation was real, but the threat wasn't: The scene Thursday was a drill designed to test an ambitious NYPD-led effort called Securing the Cities. The program aims to detect and intercept radiological devices before they can wreak havoc on Wall Street and other high-profile targets in Manhattan, the heart of the nation's largest city.
The effort also has tested the limits of domestic counterterrorism logistics, costs and tactics. It relies on the manpower and expertise of more than 100 law enforcement and public safety agencies across New York, New Jersey and Connecticut, tens of millions of dollars in federal funding and a belief that plots already set in motion can be thwarted wherever necessary.
"That includes the waterways," NYPD Commissioner Raymond Kelly said.
Security experts say such safety initiatives can't just look good on paper. To work, first responders need to be drilled constantly using mock devices and various scenarios cooked up by their superiors.
"That's what these exercises are all about - so you can be better prepared to respond when there's an actual event," said William Bratton, a Kroll security firm executive who's served as NYPD commissioner and Los Angeles police chief. "You need to identify what works and what doesn't work."
The current commissioner has a "much-needed fixation on terrorism and keeping New York safe," Bratton added.
Still, critics question whether the prevention drills are a sound use of time and resources. The Securing the Cities approach is overly reliant on the rare instances when investigators receive a tip of trouble and ignores the fact that terrorists don't have to travel outside the city to obtain dangerous materials used legitimately in the medical and construction fields, said retired Air Force Col. Randall Larsen, head of the non-profit Institute for Homeland Security.
"It's fine to do all the lights-and-sirens exercises," Larson said. "But that doesn't address what to do once a dirty bomb goes off. No one wants to do that exercise."
Police officials respond that while remaking the NYPD since the Sept. 11, 2001 attacks, the nation's largest police department has diligently trained officers on how to both prevent and respond to attacks. More than 1,000 officers are assigned to counterterrorism on a daily basis - a force that eclipses that of most entire departments elsewhere.
In the mid-2000s, the Department of Homeland Security came up with the concept of Securing the Cities to combat dirty bombs and decided that the NYPD, which currently has about 35,000 officers, was best suited to test if for the rest of the country, officials said.
The city also was chosen based on accepted wisdom that it remains a ripe terror target. In the past two years alone, New Yorkers have seen an aborted al-Qaida-sanctioned plot to attack subways with homemade explosives and a failed attempt to set off a crude fertilizer car bomb in Times Square.
By contrast, a dirty bomb - intended to spread panic by exploding and creating a radioactive cloud in urban settings - has never been discovered or detonated in a U.S. terror plot. But law enforcement considers dirty bombs a serious threat because they're easy to build and because of intelligence that foreign terrorists want to use them against American cities.
Officials also point to the case of Jose Padilla, who was accused in 2002 of receiving dirty-bomb training from al-Qaida for a potential attack. Padilla, a U.S. citizen who claimed he was illegally detained as an enemy combatant, was convicted of conspiracy in 2007 and was sentenced to more than 17 years in prison.
Securing the Cities began with a series of meetings with officials from the NYPD and 12 other larger agencies from the region, including the New Jersey State Police, the New York State Office of Homeland Security and the Metropolitan Transportation Authority Police Department. With the backing of the FBI, the U.S.
Coast Guard and various other federal entities, a plan was developed to respond to threats using checkpoints - on bridges, outside tunnels, in the water, along railways - and grid searches in and around the city.
The program has faced fiscal challenges: Proposed federal budgets in 2009 and 2010 initially withheld funding before restoring it under pressure by lawmakers. But Homeland Security has since decided that what began as a pilot project in 2006 should be permanent and could be expanded to other cities. So far, it has received $69.2 million in federal funds, which has paid for the state-of-the-art detection devices, communication networks and other equipment.
Securing the Cities planning has culminated this week in an ongoing five-day drill testing the line of defense - the largest exercise yet. The scenario in play "involves thefts of radiological material by four separate cells of a fictional terrorist group intent on targeting New York City with a dirty bomb," officials said.
Friday's drills were to involve scores of NYPD vehicles at U.N.
headquarters and increased police activity at both terminals of the Staten Island Ferry, which carries tens of thousands of people a day to lower Manhattan and the Wall Street area.
Earlier in the week, hundreds of officers who fanned out across the city and suburbs located phony devices and stolen materials at a Cadillac dealer in Westport, Conn., inside an SUV near Yankee Stadium and on three fake terrorists caught inside New York's Penn Station, one of the nation's busiest rail hubs.
On Thursday, 67 government boats were in New York Harbor, the Hudson River and other spots to monitor maritime traffic - specifically commercial and recreational boats under 300 tons - for evidence of mock bombs. The officers had been fed fictional information that radioactive cobalt and cesium had been taken from a hospital, said Capt. Michael Riggio, a coordinator from the NYPD's Counterterrorism Division.
Riggio watched as the boats, including specially designed NYPD boats with detection devices implanted in their hulls, converged on the fishing boat before officers boarded it with an array of other equipment that can further measure the threat level. The readings were transmitted by computer to a police headquarters command center and to federal scientists in Washington for analysis to help determine if the boat was indeed "hostile," he said.
Said the captain: "It's all about stopping the bad guys and weapons from getting into the city."