Emergency management experts from across the United States wrapped up a three-day meeting in New York Wednesday. The conference ended as heightened security continued citywide, following unspecified reports of a terrorist threat. Earlier in the day, police closed the Brooklyn Bridge for one hour after an unidentified object was discovered. It turned out to be an empty knapsack.

The city went on high alert Tuesday, increasing security at landmarks such as the Statue of Liberty and the Brooklyn Bridge. The two were mentioned in uncorroborated reports from the FBI that New York landmarks may be the targets of new terrorist attacks.

In addition to monitoring traffic entering the city, police have increased security on the waterways surrounding New York. Wednesday is the official opening of Fleet Week, an annual event in which thousands of navy and marine personnel gather in New York. This year, 21 naval vessels are participating in Fleet Week events. The New York Police Department has increased security zones around the vessels and around landmarks, tunnels, bridges, piers and water and ventilation systems. The security precautions came in the middle of the three-day conference devoted to emergency preparedness. Speaking to the group's closing session, former New York mayor, Rudolph Giuliani, told conference participants that they must prepare for the worst. He said he confronts people on a daily basis who tell him how saddened they are at what a dangerous place the world has become since September 11. Mr. Giuliani politely disagrees.

"The world was just as dangerous then as it is today," he said. "Even more so. We just did not know it. We did not appreciate it, we did not understand it. It was as if there was a cloud in front of us, and we did not recognize all those things that were going on."

The conference, called "Looking back, Moving Forward," focused on the lessons learned from the September 11 attack. Addressing the subject, Mr. Giuliani recounted his experience upon arriving at New York's World Trade Center as the twin towers stood burning.

"I looked up, and I saw a man jump from the 101st or 102nd floor," recalled Mr. Giuliani. "I leaned over to them and said, "This is uncharted territory. We basically have to make up our response to it."

The former mayor says there was no way to be prepared for September 11. But he says the city's preparedness for other kinds of attacks and disasters meant that, in the end, countless lives were saved, and can be saved in the future.

Still, participants in the three-day event warned that leaders must continue to improve the overall capabilities of emergency response teams and, most importantly, keep ordinary citizens from becoming complacent.