Rood said Monday the Patriot missile battery will consist of 10 interceptors capable of handling longer-range missiles fired from Iran. The plan also includes radar facilities in the Czech Republic, Britain and Greenland.

"I think the Russian government understands the limited capabilities of this system," Rood said. "We have had unprecedented discussions that have explained the technical capabilities of the system. I think, on the face of it, they understand 10 interceptors in Poland would have no impact on the Russians' strategic offensive forces."

U.S. and Polish negotiators signed an agreement on the U.S.-run missile base Aug. 20, less than two weeks after Russia sent troops into Georgian territory to back separatists in South Ossetia and Abkhazia.

"The Patriot battery in question will be a U.S. Army Patriot battery, so that it will be owned and operated by the United States Army," Rood told a State Department briefing, adding, "What we have said to the Russians is that this is not a system which is aimed at Russia, but rather is aimed at the growing threats we see from places like the Middle East."

Rood said the agreement leaves open the possibility for Russia to inspect the facilities to help build trust.