L ast month, NATO took a major step toward providing protection for its deployed forces against short- and medium-range ballistic missiles by approving more than $90 million for the development of an alliance-wide theater missile defense capability.

Protection for NATO’s deployed forces is a good first step, but it may not be enough, given that potential adversaries are working steadily to increase the range of their ballistic missiles. NATO leaders understand this and are examining options to protect European territory and populations against longer-range threats.

The United States now has a unique opportunity to encourage NATO to take this next important step by building a long-range missile defense site in Europe.

The Department of Defense has requested $3 billion over the next five years to build and deploy 10 long-range ground-based interceptors (GBIs) and associated radar in a European country at the beginning of the next decade. Such a site could provide protection for most of Europe against long-range ballistic missile threats from Iran and other locations — conceivably even against long-range ballistic missiles launched from North Korea.

Combined with NATO’s existing and planned theater missile defenses, such as Patriot, the Medium Extended Air Defense System, or MEADS, and the Aegis Ballistic Missile Defense system, this also would provide NATO robust coverage against ballistic missiles of all ranges. A GBI site in Europe also could intercept long-range missiles headed toward the United States, extending coverage and enhancing the protection provided by the national missile defense system now being fielded in Alaska and California.

The objective of fielding a GBI site in Europe can be traced back to President George W. Bush’s early policy on missile defense cooperation. As the president stated in May 2003, “because the threats of the 21st century also endanger our friends and allies around the world, it is essential that we work together to defend against these threats.” The president also announced that it would be U.S. policy to “develop and deploy missile defenses capable of protecting not only the United States and our deployed forces, but also friends and allies.”

The successful development, testing and fielding of GBIs in the United States now make it feasible to extend this defensive coverage to our allies; the growing threat from Iran now makes it essential that we do so as soon as possible.

U.S, Army Gen. Bantz Craddock, nominated to be the next commander of U.S. forces in Europe, has told Congress that “rogue states in the Middle East and Southwest Asia possess a current ballistic missile capability that threatens a major portion of Europe.” Likewise, U.S. intelligence agencies assess that Iran continues to modify its Shahab-3 medium-range ballistic missile to extend its range and effectiveness. According to Director of National Intelligence John Negroponte, “the danger that Iran will acquire a nuclear weapon and the ability to integrate it with the ballistic missiles Iran already possesses is a reason for immediate concern. Iran already has the largest inventory of ballistic missiles in the Middle East, and Tehran views its ballistic missiles as an integral part of its strategy to deter – and if necessary retaliate against – forces in the region, including U.S. forces.”

NATO leaders have understood for some time the strategic consequences of remaining vulnerable to the steadily growing ballistic missile threat. NATO’s 1999 Strategic Concept — the central alliance document underpinning NATO strategy — recognized the need for missile defense to counter nuclear, biological and chemical (NBC) threats, and noted that “the aim in doing so will be to further reduce operational vulnerabilities of NATO military forces while maintaining their flexibility and effectiveness despite the presence, threat or use of NBC weapons.”

If reducing the vulnerability of NATO forces to ballistic missiles is important for maintaining the credibility of NATO strategy, then reducing the vulnerability of NATO territory to similar threats is even more important. Imagine, if you will, the impact on NATO’s freedom of action if European homelands could be targeted with ballistic missiles armed with weapons of mass destruction.

Simply put, if alliance diplomacy and deterrence strategies are to be effective against potential adversaries armed with ballistic missiles, then the alliance must first be able to defend itself against such threats. NATO understands this, which is why in 2002, NATO Heads of State commissioned a detailed assessment of how to defend NATO population centers and territory from all types of ballistic missile threats. This study is now complete and is being considered by alliance leaders.

When NATO ministers gather this November in Riga, Latvia, I would hope that consideration is given to expanding missile defense protection beyond the theater where NATO’s deployed forces operate, to include all of NATO territory. To be sure, the alliance faces many difficult choices, while resources remain constrained. A future agreement between the United States and a European nation to field a limited long-range missile defense capability on European soil, however, could be viewed as a U.S. national contribution to the protection of European population and territory, and could reduce the cost of a broader NATO missile defense capability — should the alliance agree to move in this direction.

A missile defense site in Europe capable of providing protection for Europe and the United States against long-range threats from the Middle East and elsewhere is necessary to keep pace with the evolving ballistic missile threat; is essential for maintaining the credibility of NATO’s diplomatic and deterrence strategies; and most importantly would be critical should deterrence fail.

It would send a strong message to our allies that we remain committed to their security and would send an even stronger message to potential adversaries that the alliance will not be intimidated or coerced by ballistic missile threats directed against our homelands.

Sen. Sessions is chairman of the Senate Armed Services strategic forces subcommittee.