Police Commissioner Ray Kelly got a heads-up: FBI Director Robert Muel ler phoned Sunday night with early warning of President Obama’s pending announcement that Navy SEAL Team 6 had killed Osama bin Laden.

Kelly swallowed hard, a top aide recounted: For New York, it was “good news with complications.”

Those “complications” included the emergency security that the cash-strapped police department would mobilize to protect New York’s 8.5 million people against a possible revenge or retaliatory attack by militant Islamists.

It was a great day for America, Kelly told his top aides — especially for New Yorkers, who for a decade have been constantly reminded of that terrible September day by the vast pit where the Twin Towers once stood.

Yet bin Laden’s death has significantly increased the risk of more terrorism directed at New York, militant Islam’s No. 1 target.

Kelly immediately called Mayor Bloomberg, who was himself being briefed about the impending announcement by Homeland Security chief Janet Napolitano.

By the time the president was telling the nation of the stunning raid, the NYPD had a major expansion of security underway. A “FINEST” message instructing cops to be prepared in light of the impending announcement had already gone out to all commands. The city’s 76 precincts were ordered to increase security around station houses and take other precautions, such as paying even closer attention to suspicious packages and people.

Kelly also directed that a midnight tour of cops working transit hubs be held over, almost doubling the number of police deployed in subways and around the city’s train and ferry stations. As many as 100 “Critical Response Vehicles” holding 200 cops were ordered to rally at a designated center — a practice conducted at least twice a day somewhere in the city.

The next morning, New Yorkers emerging from rush-hour commutes in subway and train stations encountered extra police and explosive-sniffing dogs and bag-check posts throughout the city. The NYPD ordered a similar increase for the evening rush hour.

That increased presence is still in force, subject to day-to-day evaluation. While Napolitano and city officials have stressed that they have gotten no specific threat warnings that would boost the new alert system to a higher level, the NYPD is taking no chances.

The added presence of law enforcement in city streets and at iconic structures like the Empire State Building and Grand Central Station is likely to continue at least through tomorrow, when Obama is to visit the city for a ceremony at the World Trade Center site.

READ MORE: NY POST