The Obama administration signaled Sunday that it was seeking a way to interdict, possibly with China's help, North Korean sea and air shipments suspected of carrying weapons or nuclear technology. The reference to interdictions -- either at ports or airfields in countries like China or riskier confrontations on the high seas -- was made by Secretary of State Hillary Rodham Clinton. She was the administration's highest-ranking official to talk publicly about such a potentially provocative step as a response to North Korea's second nuclear test, conducted two weeks ago. While she did not specifically mention assistance from China, other administration officials have been pressing Beijing to take such action. Speaking on ABC's 'This Week,' Clinton said that the United States feared that if the test and other recent actions by North Korea did not lead to 'strong action,' there was a risk of 'an arms race in Northeast Asia,' an oblique reference to the concern that Japan would reverse its long-held ban against developing nuclear weapons. So far it is not clear how far the Chinese are willing to go in aiding the United States in stopping North Korea's profitable trade in arms. But the American focus on interdiction demonstrates a new and potentially far tougher approach to North Korea than both Presidents Bill Clinton and George W. Bush, in his second term, took as they tried unsuccessfully to reach deals that would ultimately lead North Korea to dismantle its nuclear arsenal. President Barack Obama, aides say, has decided that he will not offer North Korea new incentives to dismantle the nuclear complex at Yongbyon that the North previously promised to abandon. 'I'm tired of buying the same horse twice,' Secretary of Defense Robert M. Gates said last week, while touring an anti-missile site in Alaska that the Bush administration built to demonstrate its preparedness to destroy North Korean missiles headed toward the United States. (So far, the North Koreans have not developed that capability, though there is evidence that they may be preparing for another test of their long-range Taepodong-2 missile.) In conducting any interdictions, the United States could risk open confrontation with North Korea. Officials in Washington have been trying to find ways to stop the shipments without a conflict. Late last week, James B. Steinberg, the deputy secretary of state, visited Beijing, seeking ideas from China about sanctions, including financial pressure, that might force North Korea to change direction. 