At a recent briefing in lower Manhattan, the New York Police Department gave an auditorium full of private security executives plenty to worry about.

One of the NYPD’s intelligence analysts warned that New Yorkers have gone to fight in the Syrian civil war and could come back radicalized against the West. A high-ranking officer described drills testing the NYPD’s ability to respond to a dirty bomb attack. And a detective offered a detailed analysis of the deadly siege at a shopping mall in Nairobi, brashly challenging the Kenyan government’s claim that the gunmen were dead.

The presentations demonstrated the nation’s largest police department’s determination to stay at the forefront of counterterrorism, even as the man who spearheaded the effort — Police Commissioner Raymond Kelly — is headed out the door.

Kelly, whose 12-year tenure ends this month without a major successful terror attack on his watch, repeatedly has suggested that anyone considering remaking one of the defining initiatives of Mayor Michael Bloomberg’s administration should proceed with caution.

New York “remains squarely in the crosshairs of terrorists,” Kelly said in his final appearance at the recurring briefings. “We must do everything in our power to defend it.”

Mayor-elect Bill de Blasio and his designated police commissioner, William Bratton, plan to take a hard look at a counterterrorism operation that grew to lengths never imagined before the Sept. 11 attacks.

With the staunch support of Bloomberg, Kelly reassigned about 1,000 of the city’s roughly 35,000 officers to counterterrorism duty, posted detectives overseas to report on how other cities deal with terrorism and spent tens of millions of dollars each year to outfit the department with the latest technology, including a network of security cameras and command centers, to track suspicious activity. Kelly also put the NYPD’s Intelligence Division under the direction of a former CIA official and directed it to analyze and detect overseas and homegrown threats.

The mission has become so institutionalized at the NYPD that it “would be very difficult to dismantle it” — nor should anyone want to, said Richard Falkenrath, who led the NYPD counterterrorism unit for four years before joining The Chertoff Group security firm. “It’s an extraordinary achievement.”

Bloomberg has heaped praise on Kelly and the NYPD, mostly for overseeing dramatic declines in homicides and other conventional crimes during their tenure together. Both men have credited the controversial stop-and-frisk strategy for deterring crime by discouraging criminals from carrying illegal guns.

The mayor has spoken less frequently about the counterterrorism effort. But he has defended claims by the NYPD that it had helped uncover more than a dozen terrorism plots against the city, including what was considered the most serious attempt on the city since 9/11: a failed conspiracy by Najibullah Zazi and two former high school classmates from Queens to bomb the city’s subway system in 2008.

“I could make as cogent an argument there’s double or triple the number that were stopped, we just don’t know about it,” Bloomberg said late last year. Would-be terrorists, he reasoned, might look at the city’s beefed-up security “and say, ‘I don’t want to run that risk.’ We’ll never know.”

The campaign to protect the city has had some unintended costs: The NYPD’s Intelligence Division has been accused of interfering with federal investigations, bringing weak cases against suspected homegrown terrorists and being careless with confidential information. The division also came under fire for its surveillance of Muslims, including the secret infiltration of mosques and other tactics detailed in a series of stories by The Associated Press.

Some say it’s time to rethink the scale of the programs — and the reasons behind them.

“The philosophy that appears to be driving the surveillance programs predicated on the erroneous assumption that all Muslims are terrorists has resulted in a bloated program,” said Donna Lieberman, head of the New York Civil Liberties Union.

De Blasio has said he wants Bratton to conduct a review of the department’s intelligence-gathering operations, and he must also decide how to fill the top counterterrorism and intelligence positions that will be vacated at the end of the year.

Still, the police headquarters briefing this month made the argument that, under any administration, the city must keep devoting resources to counter a threat that isn’t going away.

As proof, police officials cited a sting last year that snared a man plotting to blow up the Federal Reserve in lower Manhattan, the arrest earlier this year of two men accused of plotting with al-Qaida to derail a train running from New York City to Toronto, and revelations in April that the Boston Marathon bombers had talked about detonating explosives in Times Square.

Rebecca Weiner, director of the Intelligence Division, emphasized the threat of homegrown extremists with no official affiliation with a terrorist group. She revealed the NYPD is trying to track New Yorkers drawn to the Syrian conflict.

“Our overriding concern is what will happen when they come back,” she said.

(AP)