Inside is a mess of hydrogen peroxide bottles, boxes of pepper, used shower caps and gloves. The counter of a small kitchen is caked in white powder; the bathtub holds vats of cooling chemicals.

At first glance it would appear like an abandoned drug lab, but that would be a fatal mistake, according to Sergeant Philip Rogan at the New York Police Department’s Counterterrorism division.

The room — which is actually a trailer in the parking lot of an unmarked counterterrorism facility in Brooklyn — is a replica of the Leeds apartment where the London bombers created five backpacks of explosives that were used to kill 52 people on July 7, 2005.

The site has already been used to train hundreds of officers to spot telltale signs of terrorist activity. Yesterday a delegation of police officials from states around New York will visit the site to learn first hand the ease with which a dedicated group of men can cause catastrophes. The police commissioner, Raymond Kelly, invited the officials to New York as part of Operation Sentry, an intelligence network of police departments in the region set up in the years after the September 11th attacks.

The four London bombers built their bombs in a rented apartment in Leeds, a city similar to Albany, with its diverse ethnic population and large number of students, Mr. Kelly said.

On the day of the attacks, the men departed early in the morning, driving first to a commuter city called Luton before taking trains into King’s Cross Station. They split up and detonated their bombs on east-, west-, and southbound trains, as well as a double-decker bus.

Just eight months after the attacks, Sgt. Rogan and five other police officers simulated the journey an upstate terrorist cell would take to attack New York City trains.

Starting in Albany, the team drove to Poughkeepsie and then took a train into Grand Central Station. They observed law enforcement, train surveillance, and the checkpoints such a group would encounter along the way. Their diagnosis was grim, but contained a shred of hope.

“We came away with the lesson that it could be done,” Sgt. Rogan said, referring to a terrorist attack in the subways. “But with training or awareness, maybe you can prevent it.”

Speaking to the delegation of police officials yesterday, Mr. Kelly said that by training patrol officers and detectives to recognize “signatures” of terrorist activity, such an attack had a higher likelihood of being stopped.

“The terrorist threat is not going away,” he said. “If anything it is going to become more dangerous.”

A former CIA official who is now the assistant commissioner of the NYPD’s Intelligence Division, Lawrence Sanchez, said the amount of radical tapes, literature and Web sites is “growing logarithmically.” With it the threat of an attack is also rising, he said.

As part of the training for officers, the police have also built a replica of the van used in the 1993 World Trade Center attack and the Oklahoma State University dorm room where Joel Hinricks built a bomb that he detonated outside a stadium in 2005. He killed only himself.