Chilling shadows from a dark future are falling upon us. The FBI assures us we can expect suicide bombers to go into action. Defense Secretary Donald Rumsfeld assures us that terrorists eventually will get nuclear weapons and make use of them. Wednesday, the Brooklyn Bridge was closed by terrorist threats. We are in a mess.

We are, in fact, in a war. However new it might be to us, it is a war.

New York City’s former mayor, Rudy Giuliani, discussed the fact of that war with the press the other day. He was answering questions after a screening of HBO’s “In Memoriam: September 11, 2001, New York City,” which will air today and will then be broadcast around the world through various CNN outlets, which should let those in other nations know just what we went through on that day.

This heartbreaking film makes clear something we must always remember about the Sept. 11 terrorists: They were not concerned about our differences in religion, skin color, sex, age, class, politics, jobs, national origin, dietary conventions or anything else. Their only intention was to kill as many of us as they could.

That is still the terrorists’ intention. They have not gone away. They will be back. You can count on that. How successful they are will depend upon what we do, what they try and how good our luck is.

Giuliani said that as mayor, he had been obsessed with terrorism since the attempt in 1993 to bring down the World Trade Center. His assumption was that there would be another attack, and he held many meetings in which potential terrorist actions were discussed. But while he could imagine planes being hijacked, he could not imagine that they would be used as missiles.

The ex-mayor dismissed the hoopla over whether President Bush knew enough to act and whether the FBI fumbled the ball. That is all easy to say from here, he noted, since “hindsight is always 20/20.”

Giuliani admitted that he is not happy that security seems to be going lax again and that people would prefer to pretend it is all over rather than continue to make demands on themselves and those whose job it is to protect them. His sense of things is that the terrorist sleepers who are surely in this country awaiting instructions will move when their masters think we least expect it.

He gives wise counsel on the issue of security, which is his strength. And I would add that in a time of such danger, we should seriously re-examine our immigration policies, find out where every Muslim who came into this country during the past 15 years is now and what he or she is doing, build as large an intelligence force in the American Muslim community as we can and make sure that everyone understands these measures are in the interest of everyone except mass murderers.

Unpleasant events and mistakes are inevitable, but this is war. And war is always some version of hell.

Stanley Crouch is a columnist for the New York Daily News. His e-mail address is scrouch@edit.nydailynews.com.