The visit comes before U.S. President George W. Bush's trip to Poland on Friday, which the Polish government says will be crucial to its decision on whether to accept the American request to base the missile defense site in Poland.
Poland has opened formal talks with Washington on its plan to place 10 interceptor missiles in the country, while the neighboring Czech Republic holds talks on another component of the system, a radar base.
The U.S. says the two sites will form part of a missile shield needed to defend Europe and North America from a potential threat from Iran.
Although polls in both countries show widespread public concern over the deployment, the Polish and Czech governments say the system should enhance their own security.
However, diplomats expect the Poles may seek additional guarantees of protection from NATO following the treats from Moscow. Western officials stress that Poles and Czechs are covered by the organization's central treaty guarantee, which states that an attack on one member is considered an attack on the whole 26-nation alliance.