The two countries also have to sign a Status of Forces Agreement (SOFA) covering the troops who would staff the base, but it has yet to be finalized.
As part of the missile defense system, the United States plans to place interceptor missiles in Poland, but talks with Warsaw have stalled.
The plans are fiercely opposed by Russia, which sees them as a threat to its national security and the international nuclear deterrence system.
"This is a very important system for Europe," Schwarzenberg said Friday. "Weapons of mass destruction and their means of delivery are proliferating in the modern world. If there are no immediate threats today, they will emerge in the future."
He said that after Russia's lease of Azerbaijan's Gabala radar station expires, its possible use could become a subject of NATO discussions.
Russia has offered the United States the use of its radar stations in Armavir in southern Russia and Gabala in Azerbaijan as alternatives, but Washington said they could only be used as "supplements," if at all.
