Washington's controversial plans, strongly opposed by Russia, have the full backing of right-wing Polish President Lech Kaczynski, whose twin brother Jaroslaw announced his resignation as prime minister on Monday following his election defeat.
Addressing foreign journalists, Tusk said his future government "has no rigid doctrine regarding the deployment of a U.S. missile defense base in the country," and that issue is "open for all arguments for and against."
The center-right politician, widely expected to pursue warmer ties with Russia and Germany than under his predecessor, said the new government would want to be certain that Warsaw will not finance a project that is not in the national security interest.
Washington is planning to deploy 10 missile interceptors in Poland and a radar in the Czech Republic as part of its European missile shield, despite Russia's concerns over national security.
The first U.S. missile interceptor could be put on combat duty in Poland as early as 2011, and the base may become fully operational by 2013.
Earlier in the day, Tusk said Poland's military contingent in Iraq should be brought home next year.
"With the approval of our most important ally, the United States, we want to reformulate our presence in Iraq," Tusk told foreign journalists. "This means ending our military mission in 2008."
President Lech Kaczynski is expected to formally invite election winner Donald Tusk to form a government later this week.