Updated

New York City, scene of the worst terrorist attack in American history, was on extremely high alert for a new act of terrorism Thursday -- one day before foreign ministers from several nations gather on the city's East Side to hear the chief U.N. weapons inspectors report on Iraq's disarmament efforts.

Officials in Washington have been warning that a terror attack against Americans could coincide with Thursday's end of the hajj, the annual Muslim pilgrimage to Mecca.

New York commuters have been experiencing extra-tight security at all crossings and tunnels in and out of the city for several days.

"I think we are all acutely aware the sad reality of today's world requires us to live with the threat of terrorism. For us here in the United States, this is a new reality," New York City Mayor Michael Bloomberg said Thursday.

"New York City is the capital of the world and we will always, unfortunately, be a target for those who hate our way of life and those who are threatened by all we hold dear."

But Bloomberg added, "we cannot allow ourselves to be paralyzed by fear. … That would destroy us without firing a shot."

On Thursday, the city's Brooklyn-Battery Tunnel was temporarily closed as police investigated a suspicious package. The tunnel connects Brooklyn with Lower Manhattan and was used to carry debris from the World Trade Center after the Sept. 11 attacks.

On Wednesday, the Bronx-Whitestone Bridge, which connects the Bronx and Queens, was also shut down while police investigated a white van.

New York City Police Commissioner Raymond Kelly said police tactics would change daily to keep potential terrorists confused. More officers are being assigned to terrorist prevention and to patrol at either end of the subway tunnels between Manhattan and Brooklyn.

About 1,200 cops in the city's counterterrorism bureau have been deployed throughout the city. These "Hercules" teams are armed with body armor and machine guns and are making their presence known in and around Times Square tourist spots, bridges and hotels.

Law enforcement also is conducting air patrols over sensitive areas such as the George Washington Bridge, Empire State Building, Statue of Liberty, Ground Zero and power facilities. The NYPD Harbor Unit has been busy patrolling the city's 500 miles of coastline day and night.

"People are bent on harming us and killing us as a nation ... that is a fact of life," Kelly told Fox News. "We're working very diligently … to see that that doesn't happen."

New York hospitals were placed on high alert based on government intelligence of a potential threat, naming cyanide as the specific terror agent.

The New York Post reported that sensors that can sniff out deadly biological and chemical agents are being tested in the city’s subway system. The shoebox-sized devices, which have been installed in hidden locations at several major stations across the city, are like fire alarms and would sound a quiet warning in the event of a terrorist attack.

"It's not cause for alarm, it should be cause for reassurance, that the plan we had is in place and I believe is the best of any city," Gov. George Pataki said. "We're New Yorkers. We're gonna get through this."

National Guardsmen stood watch under the vaulted ceiling of Grand Central Terminal. Police with bomb-detecting dogs scanned the crowd.

"Something may happen, something may not," said ad agency employee Bill McCaffrey. "You can worry about that on every street corner. It's part of living in New York."

"We're not going to back off, " Rep. Peter King, R-N.Y., told Fox News on Thursday. After Sept. 11., he said, "everyone in New York decided to fight back and we're not going to yield."

Foreign ministers from around the globe, as well as chief weapons inspectors Hans Blix and Mohamed ElBaradei, who have been searching for banned weapons of mass destruction in Iraq, will meet at the United Nations Friday to receive a full report on whether Saddam is disarming.

Blix's report will be crucial in determining whether a split Security Council calls for more arms inspections or supports U.S. calls for war.

The U.S. remained under a Code Orange "high risk" of attack status for a seventh day, and no change was in sight.

Anti-aircraft missiles guarded Washington's skies and Capitol police were told to carry gas masks at all times. They are in a small, handheld black knapsack about six inches long. Every officer has them, including those in plainclothes who provide security for leaders and in the congressional chambers.

White House security was not noticeably tighter, but some presidential aides said they were socking away water and food at home and making plans to meet up with family in the event of an attack.

In Michigan, officials stepped up security at more than 300 synagogues and Jewish institutions after the FBI warned about possible Al Qaeda attacks on Jews.

"When a threat like this comes in, we go into alert mode and we make sure that every Jewish organization in the state is notified," Betsy Kellman, Michigan head of the Anti-Defamation League, told the Detroit Free Press.

She said the front doors now are locked at most Michigan synagogues and religious schools, as well as at many of the Jewish social agencies. Visitors' identification is being checked and surveillance has been increased, she said.

The weekly FBI bulletin circulated to 17,000 law enforcement agencies urged police to be extra vigilant for possible chemical, biological and radiological attacks. FBI personnel that would react to any terrorist attacks have been told to have a bag packed for three days' deployment and put on standby.

The National Infrastructure Protection Center, which assesses and warns about threats to critical U.S. infrastructure, issued an advisory describing a heightened chance of global computer hacking.

Precautions were taken throughout the federal government. For example:

- Food safety officials were put on heightened alert but were told the threat did not involve food, said Agriculture Department spokesman Steven Cohen.

- Nuclear power plant operators were issued reminders of precautions they should take under a Code Orange.

- The Interior Department's Bureau of Reclamation has increased security at its 58 hydroelectric dams and 348 reservoirs that serve 31 million people in 17 Western states. Precautions include limiting access, closing visitors centers and roads and conducting random vehicle inspections.

The Federal Emergency Management Agency advises Americans on its Web site to purchase battery-powered radios, duct tape, scissors and plastic sheeting to cover doors, windows and vents. The agency also suggests stocking up on food and drinking water.

Citizens apparently were paying attention. Hardware stores and food clubs were reporting an increase in sales. And stores like Home Depot were bringing in more supplies to meet the demand.

But in both the nation's capital and the Big Apple, many people said they were unafraid and determined to go about their lives.

"I'm not changing our lifestyle," said Liz Davis, 43, of Alexandria, Va., who said she has plenty of food at home but has not taken other emergency steps. "Part of living near D.C. is living at a ground zero of sorts. It's part of the package."

"I find people heed the snow alerts more than terror alerts," choreographer Mindy Cooper said as she walked her dog in New York's Central Park.

Fox News' Rick Leventhal and The Associated Press contributed to this report.