LAST WEEK, George W. Bush finally came out and said it: "Leave the Cold War behind," he implored. Let us "build effective missile defenses" designed to protect "all 50 states and our friends and allies and deployed forces overseas."

With a surplus in the Treasury, the governor was bullish about overcoming the technological challenges presented by such a complex system. Afterward, all the Gore campaign could manage in reply was the robotically anodyne statement that, yes, the vice president too wants "a responsible and practical defense against a ballistic missile attack."

The Bush-Gore exchange suggests that the political battle over some sort of missile defense has now been won by the Republicans. It's just that Gore wants a national missile defense for the sake of arms control. That's why Gore's every statement on the subject comes with the caveat that a decision to proceed will hinge on a missile defense's "impact on our ability to protect arms control."

So under a Gore administration, after we get the Comprehensive Test Ban Treaty and START III in place, anything more than a bare-bones missile defense will be superfluous, since the world will -- presumably -- be safe from the nuclear scourge. In that instance, a modest battery of land-based interceptors in Alaska should do the trick, rather than the expansive schemes favored by the very same Republicans who torpedoed the Comprehensive Test Ban Treaty. Hence the need to circulate scare stories about the "massive spending" involved in developing a "scientifically unfeasible" missile defense system that will lead to the "abolition of the ABM treaty" and an inevitable "arms race."

Despite being repeated ad nauseam as self-evident truths in the media, these charges hold little water. The cost, often touted as a terrifyingly high "$ 60 billion and upwards," is not a lump sum or even a recurring cost. The Congressional Budget Office's April report found that even if the national missile defense program were expanded to Capability 3 -- the "most extensive and sophisticated stage" -- it would cost only $ 48.8 billion between its initial deployment phase in 2005 and completion 10 years later. That's about $ 5 billion annually, which includes design, testing, procurement, construction, and operations. Considering the Pentagon's budget last year was $ 286 billion, this is a small price to pay for peace of mind.

That's assuming the national missile defense works. Since April, when a joint Union of Concerned Scientists/MIT report highlighted the danger posed by enemy countermeasures, which could confuse the interceptor into thinking the simplest of decoys was a real warhead, the "scientific unfeasibility" of missile defenses has become the mantra of the opponents.

The aim of the Union of Concerned Scientists report, of course, is not constructive criticism: It is to abort any missile defense on the dubious grounds that there is no defense against the offense. French president Jacques Chirac (who opposes missile defense) recently claimed that "ever since men began waging war, you will see that there's a permanent race between sword and shield. The sword always wins." But the dialectic of warfare is far more dynamic. For every offensive weapon, there is a defensive weapon capable of being developed to mitigate its effects; and defensive superiority eventually is chipped away by a new offensive weapon.

Nevertheless, the unfeasibility argument links nicely to missile defense critics' obsession with the 1972 ABM treaty, a monument to the Doctrine of the Offensive. Once, it is true, the defensive technology did not exist to stop a nuclear strike; instead, deterrence was employed in the form of mutual assured destruction. But the ABM treaty has been overtaken by technological advances. And if the anti-missile technology exists, as Henry Kissinger rumbled after Bush's speech, then "it cannot be a strategic objective, cannot be a political objective, and cannot be a moral objective" for any president to continue promoting his country's "deliberate vulnerability" to attack. Indeed, a United States left deliberately vulnerable to missile attack will shrink from sending troops to foreign hot spots. The result will be an instinct toward isolationism and a concordant diminution of American global preeminence.

Aha! the Gore campaign counters, loosening the ABM handcuffs will spark a dangerous arms race, as Russia and China rapidly build up their nuclear arsenals in order to overwhelm American defenses. But military policy depends on political decisions, and arms races do not start of their own accord. That's why Bush was so insistent that "it is possible to build a missile defense and diffuse confrontation with Russia." If Moscow decides nuclear arms reductions are in its political interest, there can be no nuclear arms race. And Russia may so decide. After all, the recent Russian ratifications of START II and the Comprehensive Test Ban Treaty testify that Moscow is thinking politically about arms control. Vladimir Putin and his generals want to divert the billions of dollars saved by nuclear cutbacks into repairing Russia's rickety conventional forces.

The decision to proceed with a national missile defense must lie with the next president. Bush has shown he understands what is at stake, while Gore is floundering, still trying to apply outdated arms control concepts, flawed even 20 years ago, to a 21st century reality.

Alexander Rose is a columnist at the National Post in Canada.