Nato's military commander wants to draw up plans to protect its newer members - many of them ex-Soviet states - after Russia's invasion of Georgia but faces resistance from nations worried about Moscow's response, US defence officials say.
The dispute within the alliance reflects underlying tension between older members, such as France and Germany, and newer ones like Estonia, Latvia and Lithuania, who want to know how Nato will protect them from potential Russian aggression.
"This becomes politicised very quickly," said one US defence official. He said Nato's supreme allied commander, US Gen. John Craddock, started talks on defence planning with Nato's political leader, Secretary-General Jaap de Hoop Scheffer, within the past week.
The foundation of the Nato alliance is a collective defence promise known as Article 5, stating an attack on one is an attack on all. But the alliance has not written formal defence plans for some of its newer members, and those states want additional assurance from both Nato and the United States, US officials said.
"The Article 5 discussion is very much front and centre," said another senior US official ahead of this week's Nato defence ministers meeting in Budapest. Craddock has the authority to write contingency plans, but formal defence plans require a threat assessment that must be approved by Nato's political leadership. Both will be on the table at the Budapest meetings, according to US officials.
The Pentagon, which wants Craddock to write contingency plans, has sought to play down the significance of such planning, saying it is a natural part of any military alliance.
But assessing the threat posed by Russia could shift Nato's attention back to its original foe, and some allies, particularly in Western Europe, worry about the signal that would send to Moscow.
US Defence Secretary Robert Gates, with Canada and Britain, will try this week in Budapest to mediate among European allies while supporting defence planning that reaffirms the Article 5 pledge, officials said.