Roads not taken

After a great deal of analysis and debate, the United States has settled

on a national missile defense system designed to intercept missiles in mid-flight.

Other options include boost-phase interceptors, which the Russians have

proposed, and terminal-phase interceptors. During a June 20 news briefing,

Pentagon officials discussed the pros and cons of all three.

A boost-phase interceptor offers the clear advantage of knocking down

an enemy missile while the deadly debris falls onto enemy territory. No

country so far has developed a weapon sophisticated enough to do this, and

according to Pentagon officials, the United States could not field such

a weapon until around 2012, well beyond the 2005 time frame in which intelligence

sources predict a rogue nation could attack the United States.

A midcourse interceptor would have trouble discriminating between decoys

and "real McCoys," but it is technologically less challenging than the boost-phase

interceptor.

Terminal-phase interception would provide greater opportunity for sorting

out decoys but would require many more interceptors to defend all 50 states

in the late stages of an attack, possibly after dozens of submunitions were

deployed. In addition, it would be intercepting warheads — possibly carrying

nuclear, chemical or biological weapons — "right over your head."