NEW YORK – Scotland Yard alerted the New York City police department several months ago about an emerging terror plot – but it wasn’t until earlier this week that the city was warned extremists planned to explode bombs on U.S.-bound passenger jets, authorities said Thursday.

None of the 24 accused terrorists, including the masterminds of suicide bombings, were arrested in New York. And Mayor Michael Bloomberg said “to the best of our knowledge, there are no members of this group here.”

But NYPD and Scotland Yard investigators were poring over the alleged plotters’ financial, travel and phone records to uncover the network that supported them – and search for possible ties to the U.S.

“We have 1,000 police officers devoted to intelligence and counterterrorism,” Bloomberg said. “We have our own police officers around the world, including in London, where having somebody on the ground helps us in understanding what this plot was about.”

The city’s security level remained at orange, where it has been since Sept. 11, as Homeland Security officials for the first time raised the terror threat warning to Code Red – the highest level – on U.S.-bound flights leaving Britain.

New York Gov. George Pataki dispatched additional National Guard troops to Kennedy and LaGuardia airports, where there already was an increased presence of Port Authority officers.

“The efforts to protect the American people have worked exactly like they were supposed to work. New Yorkers should feel safe,” Pataki said.

The Metropolitan Transportation Authority police also stepped up security on its trains and dispatched additional bomb-sniffing dog units. The K-9 teams boarded trains at stations along Metro North and Long Island Rail Road lines throughout the day.

Bloomberg said the city would continue its robust counterterrorism measures, including subway bag searches, surveillance of bridges and tunnels and spot checks of transit hubs and other targets by heavily armed cops.

The NYPD tweaked some of its counterterrorism response based upon information coming from Scotland Yard, but the department did not beef up patrols around the city as it did after the London transit bombings.

“The nature of this plot doesn’t lend itself to the kind of added high-profile police presence that we have instituted in the wake of other terrorist plots,” Bloomberg said.

With the fifth anniversary of the Sept. 11 attacks approaching, Bloomberg said the NYPD is doing everything possible to safeguard the city.

“Let us all remember that the secret weapon that will win the war against terrorism is courage,” he said. “The best thing we can do is to continue to go about our daily lives … and show that we will not be intimidated by criminal conspiracies like this one.”

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