PERSPECTIVE ON TERRORISM : Playing on Fears of a New World Disorder : The nerve gas attack in Tokyo should be seen as an aberration; this is no crossing of the mass-psyche Rubicon.

The nerve gas attack in Tokyo’s subway raises fears that chemical weapons have now entered the arsenal of terrorism. Can biological warfare or even nuclear terrorism be far behind? Is it only a matter of time?

The Tokyo attack does not represent a new threat. Analysts and government authorities have worried for years that terrorists might employ chemical weapons. A 1985 survey of experts on terrorism indicated that 69% of them thought it somewhat or very likely that by the year 2000, terrorists would employ chemical weapons in such a way as to cause or threaten mass casualties.

Nor does the Tokyo attack demonstrate a new capability. The know-how is not a very high technical threshold--some university training in chemistry, a primitive laboratory and some protective gear.

Nevertheless, the initial reaction has been fear that the Tokyo attack, so shocking and so widely publicized, will inspire further attacks. The suggestion is that terrorists--the term is used collectively as if all the world’s terrorists were part of the same army--have crossed the psychological Rubicon, opening the way for mass murder, cities held hostage, the realization of the plot of every thriller. This is not the case.

Although the Tokyo attack may spawn a number of hoaxes and increases the probability of another actual attempt, it is not certain that terrorists will now resort to chemical warfare.

The purpose of terrorism is not merely to create mayhem. Terrorists employ violence to achieve ends other than murder for murder’s sake.

Most terrorist violence is symbolic, intended to cause publicity-attracting damage, but not death. Only about 20% of terrorist incidents involve fatalities. With the weapons terrorists have had for decades--more accessible, easier-to-use conventional explosives--they could have killed in quantity if mass murder were their sole objective. Not doing so represents a choice, not a technical limitation.

These self-imposed constraints reflect moral qualms. Even among those we label terrorist, there is concern that they be seen as a political organization or military formation as opposed to wanton killers. There is also the concern for group cohesion. A group using terrorist tactics must provide opportunities for action, but must take care not to push toward defection members who may not have the stomach for certain acts of violence. Cohesion requires consensus, and that imposes a certain conservatism on decision-making.

Terrorists also worry about alienating their perceived supporters, who they imagine to be legion if less committed than themselves. Terrorists want to provoke fear and alarm but at the same time do not want to provoke too much of a public backlash. You can’t poison the city’s water supply in the name of the popular front and expect to remain popular.

The fear of pushing governments too far is another brake on terrorist operations. A credible threat of mass destruction is likely to diminish concerns about rules that normally constrain police operations.

Chemical weapons pose further difficulties for a terrorist group contemplating their use. The consequences of chemical warfare in World War I caused widespread revulsion that led not only to an international treaty banning the use of chemical weapons but also a moral prohibition that, for the most part, prevented their use in subsequent wars. Chemical weapons remained anathema. Unfortunately, that taboo has eroded in recent years as more nations have developed chemical weapons and some have used them without punitive sanction.

Obviously, not all of these constraints apply equally to all groups. There are in every group psychopaths who invariably argue for escalation. A lengthy struggle may brutalize its participants, inuring them to higher levels of violence. Ethnic conflicts lend themselves to genocidal strategies.

Most dangerous are religious fanatics convinced that they have the mandate of God. Absolved of all moral considerations, uninterested in political mobilization, concerned with no constituency in this life, they are capable of the most violent actions. The bombing of the World Trade Center in New York, where the perpetrators clearly intended to cause a catastrophe of epic proportions, is an example.

Car bombs, like that detonated in New York, represent a trend, discernible since the 1980s, toward large-scale, indiscriminate acts of terrorism. There is, however, no inexorable progression from indiscriminate violence to mass murder, from car bombs to nerve gas.

When we look at previous examples of the use or threatened use of chemical weapons or other schemes of mass murder, we usually find not terrorist groups but deranged individuals, mad conspiracies or the collective insanity sometimes found in religious cults.

These events are aberrations, frightening in themselves, but not necessarily trends in terrorism. Even desperate men, as all terrorists are, have limits.