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.

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 of the Council of Foreign Relations, and who has also been 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 North Korea got enough plutonium for one or two bombs.

The regime expelled inspectors in 2002, giving it free rein to resume the reprocessing of the original fuel rods. North Korea also restarted operations at the Yongbyon reactor. Using satellite imagery to observe exhaust, analysts concluded that North Korea shut down the reactor on at least two other occasions for long enough periods to remove the rods and get more plutonium, says Mr. Ferguson.

The extra plutonium gathered since 2002 leads some experts to estimate the regime could have enough material for up to 10 bombs.

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

Ferguson doesn't discount the possibility that North Korea has no nuclear weapons whatsoever. "It is conceivable. It could be a grand bluff on their part.... But I don't want to challenge them on the bluff."

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.

"Nobody has a clue where the uranium program is, how big it is, or how far along it is," says John Pike of GlobalSecurity.org.

Not yet. The North has deployed Nodong 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 Taepodong 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 multiple test launches of this long-range missile have failed, including the launch on July 4 of this year.

"There's still a long way to go before they get to Alaska," says Ferguson.

Most likely. The marked similarities between North Korea's Nodong 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. 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, and may include covert facilities in hard-to-hit caves. Success in targeting could also scatter radioactive material to neighboring populations.

This is an updated version of an article that ran on Aug. 27, 2003.