How serious is North Korea's nuclear threat?

Like most of life in North Korea, nuclear programs there are largely an enigma, even to the experts. But just the possibility that the regime already possesses one or two nuclear bombs has created a crisis. Officials from the US, Japan, China, Russia, and South Korea are meeting in Beijing Wednesday to try to halt Pyongyang's development of nuclear weapons. Observers are divided on whether Pyongyang is making nukes to trade for food and fuel, or, as it says, to deter the US and its allies from invading. Either way, the North's production capability could accelerate if a freeze isn't negotiated (see chart at left).

Perhaps. The mystery dates back to 1989, when North Korea shut down its nuclear reactor in Yongbyon for 70 days. During this time, the regime removed some of the plant's fuel rods and extracted plutonium through what's called reprocessing. Plutonium is the key element needed to make the type of bomb dropped on Nagasaki, Japan, in 1945.

The regime claimed it reprocessed rods only once for a tiny amount of plutonium. But tests by outside inspectors showed several rounds of reprocessing.

"That immediately raised suspicions," says Charles Ferguson, scientist-in-residence at the Washington office of the Monterey Institute's Center for Nonproliferation Studies. "Did they separate more than what they were saying?"

Experts can only estimate how much plutonium might have been processed in that time frame. The consensus among US experts and CIA officials is that it got enough plutonium for one or two bombs. [Editor's note: The original version of this article misstated the time frame during which plutonium might have been processed.]

The regime expelled inspectors last December, giving it free rein to begin reprocessing the fuel rods. The North claims to be reprocessing now, but the US has not said publicly whether its surveillance confirms that. The rods could yield enough plutonium for six more bombs.

There are also doubts about whether they have the expertise to detonate a nuke, says Mr. Ferguson. Plutonium bombs require precision-timed explosives.

The current crisis erupted when Pyongyang admitted it had a separate program to develop a nuclear bomb based on uranium. This violated the 1994 Agreed Framework with the US, which was designed to freeze North Korea's program.

Not yet. The North has deployed No Dong missiles with a range of about 1,000 kilometers, which can strike South Korea, Japan, and US forces in the region.

A 1998 missile test that sent a three-stage Taepo Dong rocket over Japan alarmed North Korea watchers. This next-generation line of rockets, still under development, could reach Alaska, Hawaii, and perhaps the US West Coast, according to a 1998 Rumsfeld Commission report. But during that one and only test launch, the third stage failed, calling into question the reliability and accuracy of the rocket.

Most likely. The marked similarities between North Korea's No Dong and missiles in Iran and Pakistan have raised suspicions that Pyongyang is trading away its technology. As Pakistan already possesses nuclear weapons and Iran is believed to be developing them, extending the range of their delivery vehicles deals a blow to the cause of nonproliferation. But willingness to sell missiles does not necessarily mean willingness to spread nuclear know-how. Victor Cha of Georgetown University and David Kang of Dartmouth College argued in a recent Foreign Policy report that "a transfer of nuclear material would be a risky proposition for a regime that values survival above all else" given the US's preemptive mind-set.

Any military plan must face the reality that Seoul, home to over 10 million South Koreans, lies within range of North Korean artillery guns. For that reason, a counterattack by the well-armed North could be devastating. Gen. Gary Luck, a former commander of US forces in Korea, estimated another Korean War would result in 1 million casualties - 52,000 of those American.

A preemptive strike might not get all of the North's nukes. The nation's nuclear program is scattered across the country (see map), and may include covert facilities in hard-to-hit caves. Success in targeting could also scatter radioactive material to neighboring populations.

The US wants a verifiable end to North Korea's nuclear weapons program. But Washington will probably get something short of full assurance, says Ferguson. "We can't expect that we're just going to go in there and in a matter of months check all the suspect sites," he says. Given the ability of the North to hide facilities - it's estimated there are hundreds, maybe thousands of tunnels - a spirit of cooperation, fostered over time with confidence building steps, would be necessary, he argues.