The United States has started political consultations about the redeployment of its troops and bases around the world.
Undersecretary of State Marc Grossman and Undersecretary of Defence Doug Feith held talks with Nato ambassadors in Brussels on Monday.
They will begin consultations with European allies in the next few weeks.
The review is expected to result in thousands of troops being transferred from bases in Germany to new ones closer to potential trouble spots.
Ever since the falling out between the US and Germany over Iraq earlier this year, there has been talk of US troops relocating from Germany to eastern Europe.
The Cold War focus on Europe has shifted to global anti-terror actions
The details of when and how remain unclear, but the day when US troops could be permanently based in the former communist bloc may be drawing near.
Last month, President George Bush said the US was stepping up discussions with key allies in Europe and Asia about redeploying its troops and bases around the world.
The idea is to make them more mobile and better prepared to deal with threats like terrorism.
But there was also speculation that Washington wanted to punish reluctant allies like Germany by moving US bases eastwards, to countries like Poland, Romania and Bulgaria, which have strongly supported the US-led war in Iraq and also happen to be cheaper.
US Undersecretary of Defence Doug Feith indicated on Monday that the centre of gravity would indeed shift to the east, at least to some extent.
He said that the recent expansion of NATO, which has strengthened the alliance, is an important new reality.
"A lot of the current force posture in Europe is based on the realities of the Cold War, so adjustments are going to have to be made to take into account that the alliance is larger and stronger than it was a few years ago", he said.
From Brussels, Mr Feith is travelling to Poland, where Prime Minister Leszek Miller has already declared his willingness to host US bases.
Mr Feith is also planning to go to Romania, Bulgaria, Italy, Spain and Iceland, while Undersecretary of State Marc Grossman will travel to France, Britain, Germany, Russia and Turkey.
Top US generals have indicated that what Washington is looking for in eastern Europe are advance posts, rather than fully-fledged bases.
But recent press reports suggested that Washington could be deterred by the amount of investment needed to build transport and communications infrastructure in poor countries like Romania and Bulgaria.
Doug Feith answered these reports cautiously, saying that they were looking at ways of making sure that the NATO alliance remained capable and sustainable and relevant for decades ahead.
"The perspective for this exercise is decades. This is not about current events, this is not about immediate considerations, it's a matter of how we posture ourselves so that we have an alliance that's capable and sustainable going far into the future", he said.
But that, as Mr Feith stressed, means that the timetable for decisions may also take much longer than expected.
The process of political consultations will continue with a second round early next year.
The first decisions could be made by next June, at the Nato summit in Istanbul.