Transparency and collaboration. These have been Bill Bratton's buzzwords as he shapes his leadership of the NYPD.

Yet changing the department's culture after 12 years of Ray Kelly is proving a challenge. Kelly was not only the most powerful -- and largely successful -- police commissioner in city history, he also allowed no transparency and rarely collaborated.

In his first turn in 1994 under Mayor Rudy Giuliani, Bratton followed a weak mayor and a weaker police commissioner. Bratton came running out of the chute with pronouncements that portended radical change after the do-nothing culture fostered during the David Dinkins administration.

Twenty years later, Bratton is moving far more cautiously.

Let's start with collaboration. This means cooperating with other law enforcement agencies, mostly to fight terrorism. This is a subject that nearly 13 years after the Sept. 11 attacks still has New Yorkers on edge.

Bratton has been friendly toward the Port Authority police, which patrols the World Trade Center, a site Kelly fought to control.

There have been at least four meetings on security matters -- i.e., terrorism -- between the agencies' brass, including Bratton and John Miller, deputy commissioner for intelligence.

After a N.J. teenager slipped through a hole in a construction fence at 4 a.m. last week and rode an elevator to near the top of 1 World Trade Center, giving the Port Authority a black eye, the NYPD and Port Authority police were patrolling the area in tandem at 4 a.m. the following day.

"It's all done in the spirit of cooperation and sharing information," said a source who spoke on condition of anonymity to speak freely about the two agencies. "The attitude has entirely changed."

Then there is the FBI, which Kelly also fought as commissioner. That's trickier.

Perhaps the most notable bone in the bureau's throat was Kelly's decision to station NYPD detectives overseas in terrorism hot spots, where the FBI has jurisdiction. Miller spent three years as a bureau spokesman in Washington, and may be more sympathetic to the bureau's concerns.

Yet Bratton is preparing to travel to Jordan and Israel, where the NYPD has stationed detectives. Word is that he and Miller are evaluating each overseas posting. For at least the next year, the detectives are expected to remain in place, but Bratton and Miller eventually will have to determine how effective the overseas detectives have been.

In 2013, at a forum at the 92nd Street Y, Kelly acknowledged they had produced not a single lead about a potential terrorist attack on New York City.

But that's only part of the story. Are the detectives providing information to Police Plaza not found in the overseas newspapers? Are they providing insights from overseas contacts that may help prevent a future attack?

One top department official who spoke anonymously to openly discuss the program says London and Tel Aviv "are solid gold. But," he adds, "are other places just boondoggles? Were detectives sent there because those places are sources of potential information?" Or to satisfy his ego?

Now let's turn to transparency.

In Bratton's first term, the Police Foundation paid his consultant friends. One was George Kelling, whom Bratton called his "intellectual mentor." In 1994, the foundation, a non-profit, paid Kelling $25,000 to write a report on the then-ubiquitous squeegee men. Kelling, in turn, was so enamored of Bratton that in an article for the Manhattan Institute's City Journal he compared Bratton to the Greek philosopher Plato.

The foundation also paid $137,000 to John Linder, a New Mexico-based consultant who wrote Bratton's vaunted seven crime strategies. To meet a Bratton-set deadline, Linder slept on a couch in Bratton's office.

Linder's report was apparently so well done that after Giuliani fired Bratton in 1996, he hired Linder to write a $300,000 report to straighten out the city's child welfare bureaucracy.

In 2002, the foundation began paying Kelly's $1,500 annual membership at the Harvard Club, as well as his dining and entertainment expenses. This occurred after the foundation turned down his request for an American Express card.

Kelly had to amend his financial disclosure forms, which did not include the Harvard Club arrangement, after NYPD Confidential reported this perk.

In 2006, the foundation also began paying an annual $96,000 fee to Hamilton South, whose job began as a marketing consultant for the foundation but morphed into that of a high-powered public relations man for Kelly as he pondered running for mayor in 2009.

The payments for the Harvard Club and for South lasted until Kelly left office at the end of 2013.

In 2010, Kelly forced out the foundation's longtime executive director, Pam Delaney, ostensibly because she was earning more money than he was. She was replaced by her longtime assistant, Gregg Roberts, who cut off all contact with her.

Meanwhile, Valerie Salembier, a senior vice president of the Hearst Corp., became the foundation's chairwoman. She cut all contact with the media unless it had Kelly's approval.

She subsequently became an assistant commissioner in the police department's public information office.

Returning as commissioner, Bratton is again relying on Kelling, one of the framers of Bratton's "broken windows" theory of policing that marked his overhaul of the NYPD during his first term as commissioner.

Earlier this month, he and Kelling rode the subways together to learn about minor crime problems. Bratton said Kelling also would lead a survey of parks and open spots like Times Square.

Last month, Linder was seen leaving City Hall with Miller and Steve Davis, the deputy commissioner for public information.

In 2012, Bratton was hired as a consultant to the Oakland, Calif., police department. In early 2013, the city had Robert Wasserman conduct a crime-reduction study on collaborative policing in partnership with Bratton. The report contained such promises as the following: "Collaborative policing is based on Sir Robert Peel's principle #5. 'Police, at all times, should maintain a relationship with the public that gives reality to the historic tradition that the police are the public and the public are the police.' "

And: "Whereas 'community policing' focused on sending police officers into the community, 'collaborative policing' goes further by bringing the community into policing."

For this Wasserman was paid $350,000.

Last week I asked Roberts and the foundation's new chairman, Dale Hemmerdinger, whether the nonprofit is paying Kelling, Linder or Wasserman as consultants.

Neither Hemmerdinger nor Roberts returned phone calls and emails.