Some U.S. intelligence officials believe North Korea has resumed a serious effort to build nuclear weapons. Evidence from multiple sources has persuaded them that leader Kim Jong Il is pushing the construction of a new reactor -- underground, to confound U.S. spy satellites -- and trying to design usable atom bombs, possibly including missile warheads. Other analysts disagree; some Clinton administration officials think hard-liners are leaking these reports to choke off congressional support for oil shipments to North Korea, which the U.S. pledged to fund in 1994 as part of a deal that shut down Pyongyang's known nuclear program. Even if the bad news is true, the new reactor is not expected to generate more bomb-making material for several years. But if North Korea is able to design a working bomb, analysts generally believe it stockpiled enough plutonium before 1994 to build one or two of them.