President George W. Bush said on Monday he had agreed the United States would help modernize the Polish military as part of a U.S. plan to base components of a global missile defense shield in Poland.

Bush's announcement, after White House talks with Polish Prime Minister Donald Tusk, appeared to mark a major step toward meeting Poland's demand that Washington boost military aid in exchange for allowing the basing of 10 missile interceptors in Poland.

The two leaders hailed their meeting as a success but made clear that no final deal had been reached on the anti-missile system, something U.S. and Polish officials have said could still take months more.

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"The United States recognizes the need for Polish forces to be modernized," Bush told reporters. He said "before my watch is over" -- he leaves office in January 2009 -- U.S. experts would have assessed those needs.

Bush again played down Moscow's concerns about the missile shield, saying, "This system is not aimed at Russia. I will continue to work with President (Vladimir) Putin and give him those assurances as well."