The first presidential debate has drawn a clear line between George W. Bush and John Kerry on what the United States should do about North Korea’s nuclear weapons program. Except for the continuing war in Iraq, it is probably the worst security threat facing this country. Under the skillful and persistent questioning by Jim Lehrer, both nominees put it first.

Mr. Bush wants to go on with the six-nation talks, which China brokered against initial coolness by the Bush administration. The objective is to confront North Korea with a broad international consensus that it must promptly close down its nuclear weapons program. An unstated goal evidently is to pressure North Korea to bring on the downfall of its leader, Kim Jong Il.

The president’s bargaining position in the talks is to demand the dismantling of North Koreas nuclear weapons program before the discussion of any U.S. concessions. Mr. Kerry wants to go back to the one-on-one talks started by the Clinton administration. They had succeeded in 1994 in reaching an “agreed framework” for North Korea’s nuclear disarmament matched by U.S. economic and security concessions. Secretary of State Colin Powell planned to continue that track but was overruled by Mr. Bush.

Bush officials say North Korea violated the 1994 agreement. Actually both sides violated its terms and spirit. President Bush argued in the debate that a return to bilateral talks would deprive the situation of China’s influence. On the contrary, as The Washington Post pointed out, China has repeatedly asked the Bush administration to talk directly with North Korea.

Commentators often describe the North Korean leader as paranoid and untrustworthy. As for paranoia, wouldn’t an American president shudder if Mexico aimed nuclear weapons at Washington, said it loathed the American leader and wanted to topple him? As for trust, a diplomatic path lies open for a solution that would require neither side to trust the other. A task force of Korean specialists last year proposed a three-stage negotiation in which each side would make concessions, leading to a verified dismantlement of North Korea’s nuclear program, substantial U.S. food and energy aid and eventual normalization of commercial and diplomatic relations. Another important step would be ending the 1950s Korean War at last, according to the task force, which was cosponsored by the Center for International Policy in Washington and the University of Chicago’s Center for East Asian Studies.

A workable effort toward a diplomatic solution should seek to allay North Korea’s fear of a U.S. attack. At the same time it should take into account North Korea’s own interest in a settlement. North Korea, like the United States, China and South Korea, says it wants a nuclear-free Korean peninsula, yet, the explosive present situation is tempting both South Korea and Japan to develop nuclear weapons of their own.

A nuclear arms race in Northeast Asia would hurt everyone, including North Korea. So would a war intended to punish North Korea. The Kerry-Bush exchange in last week’s debate has put the North Korean nuclear program on the front burner and opened the way for a practical effort for a peaceful solution.