Poland's Cabinet has formally approved the agreement with the United States on deploying parts of a planned anti-missile system in the eastern European country.
U.S. Secretary of State Condoleezza Rice and Polish Foreign Minister Radek Sikorski are to sign the document in Warsaw Wednesday.
The United States and Poland reached agreement last week after 18 months of negotiations.
Russia strongly opposes the plan to base 10 interceptor missiles in Poland and a guidance radar in the Czech Republic, calling it a threat to its security.
But U.S. officials insist it is aimed at defending Europe from a possible attack from Iran and in no way threatens Russia.
A top Russian general said the agreement exposes Poland to the threat of attack.
The Czech Republic has agreed to accept the radar.
Some information for this report was provided by AP.
