The Terrorists Among Us : American society is all too vulnerable to attack.

A line has been crossed--we have become a vulnerable society.

Counterterrorism officials here hope that the fast work by the FBI in arresting at least two suspects, described as Muslim fundamentalists, in the Feb. 26 bombing of the World Trade Center will send a message that may discourage similar acts in the future. But the swift police work--the case was cracked in one week--cannot obscure the reality of the gaping, rubble-filled crater beneath the Trade Center. The explosion in Manhattan, which killed five and injured 1,000, was the worst major terrorist attack in the United States.

The Trade Center blast, with its direct links to the byzantine politics of the Middle East, demonstrated the enormous vulnerability of a highly industrialized, urban society to calculated acts of violence. America is a fat target. It’s infrastructure, to use a word popular these days in the Clinton White House, is vulnerable--bridges, tunnels, airports, airliners, railroads, railroad stations, communications networks, including telephone and television installations, power grids, high-rise office buildings (with windows that don’t open), hotels, apartment complexes and government offices.

It is a point not lost on foreign political leaders. Last week, the leader of the Serbs in Bosnia, Radovan Karadzic, warned that continued U.S. aid to the Muslims in that country could lead to terrorist attacks against the United States. He later modified his remarks, but the meaning was clear.

Perhaps because of the geographical barriers formed by the Atlantic and Pacific oceans, Americans have always felt somewhat protected from terror. Terror was something that happened in Israel, Beirut, Athens, Rome, Vienna, northern Ireland or London, but not in the good old U.S.A. Main Street was not the Middle East. We might have shootouts in Waco, or crazies who cut loose with automatic weapons in fast-food restaurants or post offices, but that kind of violence was at least home-grown.

But in a world that is a global village, linked by CNN and rapid telecommunications, it would seem only logical that events in remote, volatile areas overseas may have violent repercussions here at home. The case of the hundreds of Palestinians deported by Israel late last year, still encamped in a no-man’s land in southern Lebanon, is one example. Most are members of the Palestinian extremist group, Hamas. In January, federal authorities warned New York police that the U.S. Embassy in Algeria had received a warning that unless the deportees were allowed back into Israel, a target in New York City would be bombed within 48 hours. Nothing happened, and a caller extended the deadline for another 48 hours, again with no result. But New York City, with its large Jewish population, remains a tempting target for Arab or other Muslim extremists.

“The United States is a target-rich yet hostile environment for terrorism,” one high-ranking FBI official told me, speaking on condition of anonymity. The target-rich part is obvious. Why a hostile environment? “There’s a degree of geographic isolation, of course. It’s a lot more difficult for someone to engage in an act of terrorism inside the United States than it would be in Europe or Africa. But law enforcement is a major factor.” The FBI official cited the 1988 arrest, by New Jersey state police, of Yu Kikumura, a Japanese Red Army terrorist who was headed for New York City with three bombs in his car. “He was arrested at a traffic stop half an hour outside of New York because he was acting suspiciously. And the FBI has prevented terrorist acts in this country, both domestic and international, in a number of instances.”

It is also true, however, that this country’s vulnerability has greatly increased with the end of the Cold War and the breakup of the former Soviet Union and the communist hegemony over Eastern Europe. The collapse of the Soviet Union has unleashed the forces of nationalism that were suppressed as long as those nations were in the grip of communism. The civil war among Serbs, Bosnian Muslims and Croats in the former Yugoslavia is perhaps the most dramatic example, but ethnic groups are killing each other in many parts of the former Soviet Union, including Russia.

As the post-Cold War Soviet world has become much more volatile and unpredictable, the potential for violence directed at the United States has become that much greater. Not that many Americans would want to roll back democracy in Russia or Eastern Europe and restore the Cold War. But there was a certain predictability in that era, a balance of terror, as it were, as long as the superpowers held each other in check.

One month before the explosion at the World Trade Center, a terrorist attack directly linked to the ethnic strife in Bosnia took place outside Washington. Police said that Mir Aimal Kansi, a 28-year-old Pakistani, killed two Central Intelligence Agency employees and wounded two other CIA workers and a contractor for the intelligence agency as they sat in their cars waiting to turn left into the CIA’s main gate in Langley, Va., during the morning rush hour. Kansi, according to the local Virginia prosecutor, told his roommate he was unhappy over the treatment of Muslims in Bosnia, and planned to “make a big statement” by shooting up the CIA, the White House or the Israeli embassy. Kansi flew back to Pakistan the day after the shooting and is still at large, the object of an international manhunt.

One reason America is “target-rich” is that we are packed into dense, urban areas, where bombs can wreak more havoc than in a more rural nation, where the population is dispersed. According to the 1990 census, when the nation’s population stood at 248.7 million, almost 193 million Americans, or 77%, lived in metropolitan areas. Did the World Trade Center bomber(s) hope that the explosion would knock down the twin towers, in which more than 55,000 people worked?

Nor is there any shortage of terrorist and extremist groups who might mount attacks inside the United States. Mohammed A. Salameh, the first suspect arrested in the Trade Center bombing, is a follower of Sheik Omar Abdul Rahman, a blind cleric who preaches violence from his storefront mosque in Jersey City, N.J., and who was tried but acquitted in the 1981 murder of Egyptian President Anwar Sadat. He is blamed by Egyptian authorities for the current wave of violence in that country.

Aside from Islamic fundamentalists linked to Iran, there are Palestinian groups, notably Ahmed Jabril’s Popular Front for the Liberation of Palestine; Abu Nidal, responsible for airport carnage in Rome, Vienna and Karachi, and Hezbollah, the Shiite Muslim group operating in Lebanon.

Other groups include Croatian nationalists, who carried out a number of attacks in the United States in the 1970s and 1980s, among them the detonation of a bomb at the Statue of Liberty; Armenians seeking vengeance against Turks whom they claim massacred 1.5 million of their people at the turn of the century; Puerto Rican nationalists, who have been responsible for serious bombings in New York City and San Juan; the Colombian drug cartel, notably Pablo Escobar, who specializes in car bombs, although he is on the run at the moment, abandoned by his henchmen; not to mention state-supported terrorism that might be launched by Iraq, Iran or Libya.

Because of fear of terrorism, America has already changed in ways that have become so routine that they are accepted. Seven years ago, the Smithsonian Institution closed its underground parking garage, because of the possibility of a terrorist attack. There are concrete barriers in front of the White House, metal detectors at every airport. It is almost impossible to mail a letterin some airports--San Juan International, for example--because there are no mailboxes; terrorists might plant bombs in them.

Less than 24 hours before the FBI announced the arrest in the Trade Center bombing, I asked the bureau official what, if anything, could be done to ward off such attacks. “The successful solution of this case will be the best thing we can do,” he said. “So an all-out law-enforcement effort is under way to solve this. We can’t just say, ‘OK, we join the rest of the world as victims of terrorism.’ ”