America’s missile shield passed an important preliminary test high over the Pacific Ocean Saturday. Although the prototype interceptor launched from the Marshall Islands was guided to the incoming mock warhead and away from the accompanying decoy by helpful infrared signals that won’t be replicated by any enemy, this hitting a bullet with a bullet – at speeds far exceeding those of any earthbound bullet – was an impressive technological feat.

On Monday, back on Earth, Russian President Vladimir Putin and Chinese President Jiang Zemin signed their countries’ first friendship treaty in more than half a century. Although the treaty is now little more than a handshake and a promise, this re-energized strategic partnership clearly is driven by that missile shield test. The opposition by old Cold War foes to the National Missile Defense project, when combined with equally strong opposition by old Cold War allies in Europe, creates a challenge for the Bush administration that goes far beyond technology.

The technology is the easy part. More tests remain, many more, but it is hard to imagine the formidable scientific and engineering challenges not being met given the amount of money being thrown at them. Some $50 billion already has been spent in the last 12 years on what is now called the National Missile Defense project; the Bush administration seeks $8 billion for next year, an increase of more 50 percent above the appropriations of recent years. Even multiple warheads and truly deceptive decoys are not likely to withstand such an onslaught.

Diplomacy is where this gets difficult. The 1972 Anti-Ballistic Missile Treaty between the United States and the now former Soviet Union explicitly prohibits deploying what this project intends to produce. Yet the Bush administration says it intends to build a new facility for ground-based missiles in Alaska that it would use for testing and admits that this construction could amount to deployment, because the facility could be used to field a preliminary defense system within three or four years. The administration also says its testing will conflict with the ABM within months. But it does not say what specific test will trigger the violation, when it will happen or whether it will occur following an amendment of the treaty or a unilateral U.S. abrogation of it.

A missile shield could protect the world from the growing nuclear missile capabilities of such nations as North Korea and Iraq only if it meets two conditions that will genuinely increase global stability. First, of course, it must work under hostile conditions, not just conditions designed to produce successful tests. Second, it must be done under an amended agreement with Russia.

The administration, however, suggests that it will give Russia a few months to agree to amend the ABM Treaty or the United States will scrap it unilaterally, thus betraying a failure to understand the most fundamental concept of diplomacy. The sight of the presidents of those former Cold War foes shaking hands suggests what such a failure could bring.

The ABM Treaty worked for 29 years; it is the glue that held the old security framework of Mutually Assured Destruction together. Despite suffering from an unfortunate yet appropriately chilling acronym, MAD made sense – without a missile shield to protect from retaliation, no nuclear power would dare launch a first strike. Building a new missile shield requires building a new security framework and the framework, as in all sound construction, must come first.