Polish concerns
Bush has visited Poland three times in his seven years as US president, a measure of his appreciation for Warsaw's steady pro-American stance underlined by the hundreds of Polish troops who have served - and in two dozen cases - died in Iraq.
But that alliance has undergone a serious reassessment since last October when Polish voters threw out the conservative government.
But he has put Washington on notice not to expect quick or easy approval of its missile plan.
"I understand that America cares about its own security and I share the opinion that the security of America effects global security," he said.
"But Poland lies in a specific location and has a very specific history which means that we need to seriously consider concrete, and measured aspects of security when it comes to such critical events in the region."
Bush admitted "there's a lot of work to do because many times a strategy on paper is a little different from the details so our experts are working through the system to make sure the people of Poland are comfortable with the idea".
The Poles have also said they are wary that they could pay a heavy political price if a Democratic president succeeds Bush and decides to abandon his European missile shield concept.