U.S. President Barack Obama came under a fusillade of criticism from missile defense advocates following the announcement Sept. 17 of a change in U.S. plans for a European shield, which was to feature 10 ground-based interceptors in Poland and a powerful tracking radar in the Czech Republic. The new plan calls for deploying Aegis ships equipped with Standard Missile (SM)-3 interceptors to defend Europe from short- and medium-range Iranian missiles starting in 2011 and gradually upgrading capabilities — including the addition of land-based SM-3 variants — to address the threat as it evolves.

Some of the harshest remarks came from U.S. Rep. Trent Franks (R-Ariz.), founder and co-chairman of the U.S. House Missile Defense Caucus. In a press release that cast the decision as an “abandonment of European missile defense,” Franks said the president had “disgraced the nation by breaking his word to loyal and courageous allies in the Czech Republic and Poland.” Other members of the caucus accused the administration — albeit in less inflammatory terms — of appeasing Russia, which had vociferously opposed the previous U.S. plan.

Calling the change a betrayal of America’s European allies is a good example of the hyperbole that all too often takes the place of rational debate on politically tinged topics like missile defense. In fact, the new plan offers protection for Europe sooner against what everybody agrees is an existing threat: Iran’s growing arsenal of short- and medium-range ballistic missiles. What gets deferred is the ability to defend U.S. territory — at least with interceptors based on European territory — against Iranian ICBMs, a threat that U.S. Defense Secretary Robert Gates said is developing more slowly than previously estimated.

The appeasement charges are a bit strong as well, although it is difficult to believe, as Mr. Gates suggested during a Sept. 17 press conference, that Russia’s objections to the previous plan did not factor into the administration’s calculus. Mr. Gates restated the administration’s desire for Russia to become a U.S. partner in a missile defense scheme for Europe, something that in all likelihood was a non-starter under the old plan. The agreements by the Polish and Czech governments to host U.S. missile defense installations had not been ratified by the nations’ respective parliaments, and ratification was by no means a certainty. Nevertheless, the Obama administration must take concrete steps to reassure these governments — who no doubt feel more threatened by Russian encroachment than by Iranian missiles — that their decade-long membership in NATO means something.

The White House also needs to provide realistic long-term cost estimates for the new plan. The president clearly is looking to rein in missile defense spending, which soared under his predecessor, and on its face, the new plan appears cheaper in the near term because it utilizes existing assets. Further, as U.S. Marine Corps Gen. James E. Cartwright, vice chairman of the joint chiefs of staff, pointed out during the press conference, it also leverages ongoing development programs, such as the SM-3 Block 2 interceptor being developed jointly with Japan.

But Gen. Cartwright’s per-missile cost comparison of the old and new plans was less than enlightening. He noted that an SM-3 costs anywhere between $9.5 million and $15 million depending on the variant, whereas the ground-based interceptors now installed in Alaska and California — from which the two-stage interceptors in Poland were to be derived — cost about $70 million each. Far more instructive is a comparison released in February by the Congressional Budget Office (CBO), which said defending Europe using three Aegis ships equipped with SM-3 Block 2 interceptors would cost twice as much as the now-abandoned approach, or $18 billion-$22 billion  versus $9 billion-$13 billion, over a 20-year period.

Moreover, Mr. Gates said development and testing of a two-stage ground-based interceptor would continue under the new plan, which presumably would add to its cost. So, too, would developing and deploying by around 2020 another SM-3 variant that would be capable of hitting ICBMs, which is now part of the official blueprint.

But if the CBO study revealed more about the potential long-term cost of Mr. Obama’s plan than perhaps he would have preferred, it also made a point the president’s most vehement critics have ignored: The interceptors already in place in Alaska and California would protect nearly 100 percent of the U.S. population from an Iranian missile strike. Setting aside the dubious assumption that Iran’s leadership would invite Tehran’s annihilation by openly attacking a U.S. city, the ability to defend U.S. territory is the primary distinction — at least in terms of capability — between the new and the old plan for the European shield.

Over the years, much of the missile defense debate in the United States has been framed on one side by ideologues who never saw a missile defense spending program they didn’t regard as absolutely necessary — no matter how farfetched — and on the other by unyielding skeptics who never believed the concept could work.

Neither position holds up. Hit-to-kill technologies such as the SM-3 are proving viable and clearly have a role to play in U.S. and allied security. At the same time, missile defense is not a Holy Grail; the technology will never be infallible, and missiles are not the only — or necessarily the most immediate or gravest — threat out there. The debate in the months and years ahead should focus on which systems have the best chance of success against the likeliest threats, recognizing that there are other security priorities that are equally — and in many cases more — deserving of the Pentagon’s limited resources.