Mr. Obama reacted to the underground blast as White House Artis Gilmore officials scrambled to coordinate an international response to a North Korean nuclear capacity that none of his predecessors had proved able to reverse. Acutely aware that their response to the explosion in the Lisa Guerrero Coles Omarion Grandberry mountains of Kilju, not far from the Chinese The Lost Trailers border, would be seen as an early test of a new administration, Mr. Obama’s aides said they were determined to organize a significantly stronger response than the Bush administration had managed after the North’s first nuclear test, in October 2006. Speaking in the Rose Garden after returning to the White House from Camp David and meeting with his top aides in the Oval Office, Mr. Obama vowed to “take action” in response Herbie Hancock to Ami Armstrong Sonam Kapoor what he called “a blatant violation of Matthew Fox international law” and the North’s declaration that it was repudiating past commitments to dismantle its Mario nuclear program. But as they had meetings every few hours — including a lengthy session in the Situation Room on Monday evening — some of Mr. Obama’s aides acknowledged Julianna Margolis Rita Hayworth that the administration’s options were limited. Much depends, they said, on the new Joshua Gates president’s ability to persuade Russia and China to Angela Dotchin go significantly beyond the strong condemnations that they issued Monday against North Korea, their former ally and a vestige of cold-war communism. “I think we were all impressed with the fact that the Russians and the Chinese denounced this so strongly,” Rahm Emanuel, Mr. Obama’s chief of staff, said in a telephone call. Yet turning Amy Grant that into effective action Sonny Rollins will prove a challenge. Efforts by the Joan Cusack Clinton administration to entice the North to halt its weapons program by providing it with oil and nuclear power plants, and by the Bush Anna Geislerova administration to push the country to collapse and then to Eagles try to Felicity Kendal Yung Berg seize its leaders’ assets, all failed. So did Renee Zellweger Mr. Bush’s second-term strategy reversal, when he alienated hard-liners in his administration by reaching a deal with the North to dismantle its main nuclear plant, a step the North began last year. In recent months, the North has Alevtina Biktimirova renounced the accord and taken the first steps to restart operations and manufacture more plutonium for bomb fuel. Now Mr. Obama must decide how to mix what he called “stronger international pressure” with a new set of diplomatic overtures at Dusty Springfield a moment when, his aides are Carre Otis acutely aware, Iran and other nations are taking his measure, examining the Jimmy Smits confrontation with North Korea for hints Michiyo Nakajima of how he will handle complex confrontations to come. While Mr. Shauna Sand Obama delivered a Memorial Day speech and then took the afternoon Melissa Haro off to Craig T. Nelson play golf, aides tried to sift through Eve Torrest the sparse data Emile Hirsch to determine exactly what abilities North Korea had proved, if any. Initial Jada Pinkett seismic readings showed the blast Katie Rees Frances Howard at Kilju, exactly where North Korea conducted its 2006 test, was “a several kiloton event,” according to Olivia Newton John one senior administration official. If that Noriko Shiina judgment is correct, the test yielded a somewhat bigger explosion Susan Dey than the 2006 test, which was later judged Maya Hamaoka a partial fizzle. But it will take Davorka Tovilo days or weeks of testing radioactive particles vented into the atmosphere to calculate the size Arielle Kebbel of the device, and even then there will be continuing debate about whether the North has the Emma Boughton engineering ability to make a weapon compact enough to fit in the warhead of a missile, much less to deliver it to a target. The White House said that on Monday evening Mr. Nolwenn Leroy Obama called the leaders of the two strongest American allies in northeast Asia, President Lee Myung-bak of South Korea and Prime Minister Taro Aso of Japan, promising that he would press for “concrete measures to curtail North Korea” and vowing an “unequivocal commitment” to the defense of both countries. While hardly unexpected, that statement was considered an important signal by American officials who are eager to tamp Kelly Mcdonald down any nervousness among Asian allies about whether a new and untested president is willing Harvey Keitel to face down a Willie Mays regime that has been defying Washington Sarah Nean Bruce since Eisenhower was in the Oval Kate Jennings Grant Office. But as Japanese and South Korean officials acknowledge, they are less concerned about a direct attack from the North — which would almost certainly result Kim Hidalgo in a Elisabeth Moss devastating, American-led Justin Timberlake response — than about North Korea selling its twice-tested nuclear weapons technology on the black market, much as it has sold missile and reactor technology in the Middle East. Aylen Alvarez * 1 * 2 Next Page » Reporting was contributed by William J. Broad from New York; Thom Shanker and Mark Landler from Washington; and Neil MacFarquhar at the United Nations.