As part of the New York City Police Department’s lobbying efforts to have tougher restrictions put on the sale of a dangerous chemical that can be used in bombs, it set up a clandestine operation to demonstrate just how easily terrorists can get their hands on chlorine.

Under the guise of a front company, the police department’s counterterrorism unit was able to purchase three 100-pound highpressure tanks of chlorine from a private distributor in June 2007 via the Internet without providing proper identification.

“We’re especially concerned about this lapse after Al Qaeda began combining chlorine gas tanks with conventional explosives in Iraq in 2006 with the goal of inflicting greater mass casualties,” the police commissioner, Raymond Kelly, said yesterday.

With information and the results from the investigation, which was named Operation Blue Cloud in reference to the color of chlorine gas, the police department made a videotape that was sent to the U.S. Department of Homeland Security two weeks ago. It was shown publicly yesterday for the first time to a group of private security executives.

The Department of Homeland Security is currently creating regulations concerning security at chlorine manufacturing plants, and the police department is asking it to include strict “know-your-customer rules,” Mr. Kelly said.

Terrorists in Iraq have increasingly used chlorine in bomb making. At least 10 attacks in Iraq had been perpetrated using chlorine canisters as of June 2007, according to a U.N. report released last year.