Czech Prime Minister Mirek Topolanek made the announcement in Warsaw following talks with his Polish counterpart Jaroslaw Kaczynski.
"Both of our countries are now preparing a response to the U.S. proposal," Topolanek said. "We have agreed that both countries are likely to give a positive response, and then we will begin negotiations."
The project, unveiled by Washington last month, calls for a radar station to be deployed in the Czech Republic and missiles in Poland by 2012.
Both Prague and Warsaw had previously expressed interest in the U.S. proposal. But the February 19 statement offered the clearest indication of agreement so far.
The two prime ministers reiterated that the system, which the United States says is intended to intercept potential attacks from "rogue" states, is not aimed at Russia.
Their assurances did little to soothe Moscow, which has vehemently objected to having the shield on its doorstep.
Russian Foreign Minister Sergei Lavrov today reiterated Moscow's concerns.
"We are seriously concerned about plans to deploy elements of a U.S. missile-defense system in Europe and the critical situation that threatens the Conventional Armed Forces in Europe Treaty," Lavrov said.
"NATO's enlargement, which is undertaken despite the assurances we were given previously, does not help strengthen trust either. We are also concerned about the advance of the alliance's infrastructure toward the Russian border."
Nikolai Solovtsov, the commander of Russia's Strategic Missile Forces, said on February 19 that Russia may withdraw from a 1987 treaty with the United States limiting short- and medium-range missiles in Europe if the U.S. plan goes ahead.
Solovtsov also warned that hosting the U.S. shield could make the Czech Republic and Poland targets of a Russian missile strike.
"If there is a political decision [made by Russia] to withdraw from [the Intermediate-Range Nuclear Forces Treaty] that was signed between the United States and Russia, the Strategic Missile Forces will be capable of carrying out this task [targeting sites in the Czech Republic and Poland]," Solovtsov said.
This was one of the toughest comments yet by Russian officials on the issue since President Vladimir Putin warned of a "new Cold War" in a speech in Munich on February 10.
New Arms Race?
NATO dismissed Solovtsov's remarks as "extreme language" and said they were "uncalled for."
Military experts say that the planned U.S. shield would not actually be capable of stopping Russian missiles.
But Aleksandr Pikayev, a senior analyst at the Moscow-based Institute for World Economy and International Relations, tells RFE/RL that Moscow is concerned such capabilities might be reached after the system is in place.
"There is a both a political and military danger here," Pikayev said. "This would be the first time since the end of the Cold War that an extensive U.S. armament system that can potentially intercept Russian nonstrategic missiles has been deployed close to Russian borders. Concerning Russian strategic missiles, it probably won't pose any threat initially. But with time, as antimissile systems are perfected, this capability will be achieved."
Russian military expert Aleksandr Golts, however, says Moscow's angry reaction is less about security concerns than about what it perceives as Washington's attempt to impose its will on the world.
"The U.S. antimissile defense system does not threaten Russia's nuclear potential," Golts said. "Moscow considers that what is happening diminishes its status as a great nuclear superpower, and this is why it's reacting so harshly."