After pursuing atomic weaponry for the better part of a generation, it now appears that North Korea has finally clawed its way into the "nuclear club." And that means that the global strategic game has changed forever. North Korea, which was barely tolerable to the major Asian powers back when it was merely a potential troublemaker, is now a real and present danger. The time for negotiations is over. Now it's about containment and deterrence.

Assuming Monday's underground explosion is deemed to have been a successful nuclear test, North Korea is now the world's ninth nuclear power. Although its leaders may think that translates automatically into regional strength and increased global respect, it's time to show them what they've really won: unflinching international scrutiny and a spot at the top of Washington's list of nuclear targets.

Kim Jong Il has entered a new era, one in which his pattern of brinksmanship, instead of extracting aid from his neighbors, risks provoking a nuclear holocaust. It is critical that Washington and other powers make crystal clear the responsibilities that come with North Korea's decision: A nuclear power must not bluff, must not provoke and must not make threats lightly. In contrast to the ambiguous behavior and bellicose rhetoric they've displayed in the past, North Korean leaders must now avoid steps that could lead to miscalculation and unintentional conflict.

As long as Pyongyang's weapons capability was in doubt, the world could avoid answering the tough questions: Can we really live with a nuclear North Korea? How can we deter a country we don't really understand?

The United States must ensure that North Korea's leaders understand the full force of our commitment to defend our Asian allies. President Bush's statement that the United States will hold North Korea accountable for its actions is a good first step. However, it took the United States years of face-to-face talks with the Soviet Union and China to work out a stable relationship based on mutual deterrence. Washington will have to find ways to ensure that Pyongyang does not overreach or miscalculate with its nuclear capability.

However distasteful the Bush administration finds direct talks with North Korea, the president should nonetheless dispatch a personal envoy to Pyongyang with a clear message: Any attempt to use its nuclear arsenal offensively will bring immediate, disastrous and possibly nuclear consequences. Further, Kim needs to understand that any future North Korean missile tests that are not announced or that are aimed at or over U.S., South Korean or Japanese territory might warrant a U.S. nuclear response. That's because it would be impossible for any U.S. leader to be sure that such "tests" were not the first signs of a nuclear attack.

This envoy would not be empowered to negotiate. The six-party talks were moribund before and should be declared dead. The envoy's job would be merely to deliver an unambiguous, sober message about Pyongyang's new responsibilities. The Bush administration will undoubtedly try to step up the economic and political pressure on Pyongyang to disarm. But the naval blockade that it is contemplating is unlikely to succeed either in forcing North Korea to reverse course or in preventing it from exporting its nuclear weapons should it choose to do so.

Fortunately, the fear that Pyongyang will try to export its nuclear weapons is not terribly realistic. Although it's true that North Korea has sold missiles to Pakistan, Iran, Syria and Yemen, it's unlikely Kim would be rash enough to sell his nuclear jewels to the highest bidder, knowing that the world could trace any nuclear bomb back to him by its radioactive signature. Just in case, however, the envoy should make clear that any export of nuclear weapons or materials would force the United States to re-evaluate whether attacking North Korea, however horrific, would be preferable to allowing it to proliferate.

Other financial sanctions against North Korea may be in the offing, but China is now even less likely to risk the collapse of a nuclear North Korea, for fear that the weapons might fall into the hands of North Korean military elements that are even less responsive to Chinese interests than Kim is.

Having watched the U.S. accept China, India and Pakistan as nuclear powers, Kim probably reasons that he will eventually be an accepted and respected member of the nuclear club if only he waits long enough. (Tehran's calculations are probably the same.) But he might be whistling past the graveyard. China and India are each a billion people strong — too big to ignore or antagonize. Pakistan, while smaller, is only accepted because it's seen by Bush as indispensable to the global war on terrorism. Had al-Qaida never attacked the U.S., Pakistan might well be high on the list of states deemed ripe by the Bush administration for regime change — though its nuclear weapons would have forestalled a U.S. invasion.

Pyongyang enjoys no such clout. It's an economic basket case; no American businesses are panting to get in, and even South Koreans will be forced to rethink their engagement policies. The only interest the world can have now with North Korea is in avoiding Armageddon.

Jon B. Wolfsthal is a fellow at the Center for Strategic and International Studies. He wrote this commentary for the Los Angeles Times.