David A. Hamburg, a psychiatrist specializing in behavioral biology, has suggested that fear is the cause of war. In a lecture series at the American Museum of Natural History, Dr. Hamburg noted ''the human tendency to react with fear and hostility to strangers'' and concluded: ''We justify our slaughter of outside groups by our need to protect our own.''
Thus the frontier of 1983 sciences brings Dr. Hamburg almost abreast of the Greek historian Thucydides, who wrote some 2,400 years ago that what makes war ''inevitable'' is ''power'' and ''the fear which this inspires.'' On the subject of war we seem to be unforgivably slow learners, considering the ghastly price the human race has paid for stumbling into one slaughter after another.
Thucydides was hardly a pacifist. He ranked as a general in the conflict to which he played historian - the Peloponnesian war between Athens and Sparta. But nobody, including behavioral biologists, has ever been more clear-eyed about the small steps - the ritual dances - that lead a society ruled more or less by reason into the frenzy of tooth-and-claw combat:
1. ''Antecedent grounds of complaint'' are recited by one community to another - the litany of ''old grievances.''
2. One depicts oneself as ''inoffensive, a victim to the injustice of others.''
3. One depicts, on the other hand, ''the violence and rapacity of our opponents.'' We would consider it ''disgraceful to trample on their moderation.'' But where is their moderation? We see no sign of it.
4. In fact, one begins to see one's opponent as a sinisterly alien breed of men - ''how widely, how absolutely different from yourselves.''
5. Urgently obeying ''the law of self-preservation,'' one arms oneself to the teeth against this ''aggressive'' people. ''Arbitration'' becomes a ''specious word'' - a stalling tactic.
6. When ''the preparations of both the combatants'' are ''in every department in the last state of perfection,'' each side looks for ''as good a pretext for war as possible.'' By now, almost anything will ''amply justify'' a first strike.
And so, according to Thucydides, fear finds its tribal art form: war.
As a military man, Thucydides does not oppose an armament program, or even war. He simply chronicles with a Greek tragic-shrug how the military enterprise can take control of the planners, like a runaway fire.
What can be done before ''the entire social fabric becomes fuel to feed the devouring flames,'' in the words of the English historian Arnold Toynbee, a close student of Thucydides? Thucydides was a pragmatist rather than an idealist. He would have been skeptical of the deterrent of love, or even the commandment: ''Thou shalt not kill.'' But he would have understood and appreciated the tough-minded resistance of the three business groups (the National Association of Manufacturers, the National Federation of Independent Business, and the American Conference of Business) who joined last week to advocate a reduction of $18 to $23 billion in the defense budget - seconded a day later by the Bipartisan Budget Appeal, led by five former secretaries of the treasury, recommending a cut of $25 billion.
For Thucydides was one of the first to state the argument of enlightened self-interest, revived by both these new alliances: What good does it do to build a magnificent machine of destruction to protect one's valued way of life if the process is so costly and debilitating that it lays waste this way of life as surely as if one's enemy triumphed on the battlefield?
The money, energy, and imagination dedicated to the strategies of war will continue to exceed the resources devoted to its prevention. But it can be taken as a cautiously hopeful sign that practical men want a balance of power against militarism in their own state, in the same way that their military men want a balance of power against other states. May we dare hope that such Thucydidean pragmatists exist in 1983's version of Sparta as well as in 1983's version of Athens?