Ballistic missile defense began as Ronald Reagan's grandiose ''star wars,'' the shield against a massive Soviet nuclear attack. That was largely abandoned because of failures, costs and the end of the Cold War. The concept has been revived in recent years as a ''thin'' defense against a few missiles fired by a terrorist nation. A decision about whether to move ahead to deployment is scheduled for the summer. One benefit from the end of the Cold War was the disappearance of the intricate deterrence calculus that had been necessary when nuclear war between the United States and the Soviet Union was a real danger.
Risks still exist, but they are mostly new risks.
The renewal of the ABM effort, while failing to meet these new risks, is scaring the old nuclear states back into the old fears. After the defeat of the test ban treaty in the Senate, it has renewed worries about the superpower in the china shop. China, fearing that a U.S. missile defense will decrease its ability to counter some future American aggression, says it will respond by accelerating its nuclear buildup. China can already mount a plausible threat to hit the United States with a few nuclear warheads, but, unlike the Soviet Union during the Cold War, it has no power to prevent annihilation in return. Marginal changes in the balance will have little effect for many years.