THE HAGUE, Netherlands -- President Barack Obama vowed on Tuesday that the United States would use its military to come to the defense of any NATO country that is threatened, sending a warning to the Russian president, Vladimir Putin, about the consequences of further aggression along the border with Eastern Europe.
"We will act in their defense against any threats," Obama said at a news conference in The Hague. "That's what NATO is all about. When it comes to a potential military response, that is defined by NATO membership."
The president said the United States and other world powers rejected Russia's annexation of Crimea, a region of Ukraine that voted to secede on March 16. But he acknowledged that military force would not be used to return that region to Ukraine, which is not a member of NATO.
"There's no expectation that they will be dislodged by force," Obama said of the Russian forces in Crimea. He said the world was limited to trying to use legal and economic pressure against Russia. "It would be dishonest to suggest that there is a simple solution to resolving what has already taken place in Crimea."
But Obama quickly added, "History has a funny way of moving in twists and turns, and not just in a straight line."
He also said his plan to let bulk telephone data records remain in the hands of communications companies would allow the government to effectively combat terrorism while eliminating concerns that law enforcement could abuse the database to invade people's privacy.
A day after leading a meeting of the industrialized democratic nations known as the G-8 group until Monday, when members voted to oust Russia, Obama accused Putin of acting from a position of weakness in Russia's aggression against Ukraine.
"The fact that Russia felt compelled to go in militarily," Obama said, "indicates less influence, not more."
The president said Russia's buildup of troops on its border with Ukraine appeared to be "intimidation," while acknowledging that "Russia has a right legally to have its troops on its own soil."
But Obama rejected an assertion made during the 2012 presidential campaign by Mitt Romney, his Republican challenger, that Russia would be the "No. 1 geopolitical foe" for the United States in the years ahead. He said Russia was largely a threat to its neighbors, not to the United States.
He said he continued to be more concerned about "the prospect of a nuclear weapon going off in Manhattan."
On the telephone records, Obama said the proposal he intended to submit to Congress "ensures that the government is not in possession of this bulk data."
He added, "I'm confident that it allows us to do what is necessary in order to deal with the dangers of a terrorist attack, and it does so in a way that deals with the concerns."
By MICHAEL D. SHEAR and ALISON SMALE
The New York Times