What if North Korea tests a nuclear bomb?

In all its years of saber rattling and boasts of nuclear-weapons capabilities, North Korea has never gone beyond talk to proving that it has the bomb.

Now Pyongyang says it will conduct a nuclear test – a move that would remove any doubt about the accession of the secretive and volatile regime of dictator Kim Jong Il to the nuclear club. With no international inspectors having set foot in the country for four years, a test would provide clues about the kind and power of weapons and the level of technology it possesses.

"At a minimum, a test would be a clarifying moment," says Jonathan Pollack, director of the Strategic Research Department at the Naval War College in Newport, R.I.

In addition, a test would hold geopolitical ramifications for the northeast Asian region, experts say, and for international efforts to keep the proliferation genie in its bottle. "The political effects of a nuclear test would be at least as consequential – and destabilizing – as any technological leap it might provide the North Korean nuclear program," says Daryl Kimball, executive director of the Arms Control Association in Washington.

A test would shake up northeast Asia, sending shock waves through South Korea and possibly inciting a regional arms race – causing Japan and even South Korea to consider it a necessity to reverse course and develop their own nuclear deterrents. That, experts say, would very likely mean that the international nonproliferation regime is dead.

North Korea has claimed since 2005 that it has a nuclear arsenal, and intelligence specialists believe Pyongyang probably possesses enough plutonium for as many as 10 average-size plutonium bombs. A missile test Pyongyang conducted this summer demonstrated its continuing progress in missile technology, but experts say it still does not have the capability – or a miniaturized weapon – to deliver a weapon by missile.

The only way North Korea at this stage could stage a nuclear attack would be to drop a bomb from an airplane that might be detected as it left North Korean airspace. Besides, notes Mr. Kimball, the North does not possess anything like the B-29 the US used to deliver the first nuclear weapon to its target.

"Their bomb is a standard bomb comparable to the one on Hiroshima," says Kim Tae Woo, senior fellow at the Korea Institute for Defense Analyses, an adjunct of the defense ministry in Seoul. The Hiroshima bomb, dropped on the Japanese city of Hiroshima on Aug. 6, 1945, had an explosive effect of 12.5 kilotons, while the one dropped three days later on Nagasaki had an impact of 20 kilotons.

"They have missiles capable of mounting nuclear weapons," says Mr. Kim, "but they should continually minimize the size of weight" so the warheads are small enough for missiles to be able to carry them long distances.

Analysts in South Korea say a nuclear test by the North could cause Seoul to reconsider its policy of reconciliation with Pyongyang.

Still, many observers say North Korea's new threat is primarily directed at the United States – designed to pressure the US into calling off financial sanctions that have been hurting the North, and accepting the direct talks, and the security guarantees, that Pyongyang wants.

Washington's response since North Korea announced its intentions Tuesday has been deliberate but nonreactive, with Secretary of State Condoleezza Rice saying a test would be "provocative."

The United Nations Security Council was to take up the North Korean issue Wednesday. Some experts see UN Ambassador John Bolton's call for "preventive diplomacy" toward the North as a desire by Washington to use Pyongyang's threatened test to fortify the international front of powers, including China and Russia, to deal more forcefully with the Kim regime.

Alarm over North Korea's nuclear program stems mainly from its more advanced plutonium-weapon development. But Pyongyang is also working on uranium enrichment technology, though less is known about its progress in that area, say intelligence and weapons experts.

"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.

The Bush administration confronted the regime with evidence of uranium enrichment activities, which the regime reportedly acknowledged – then denied.

The US and other nations need to think in terms of North Korea's global threat as much for its potential to sell nuclear technology and materials as for its future ability to deliver a weapon to a target, says Mr. Kimball of the Arms Control Association. North Korea's regime has already shown a willingness to sell technology and materials – in particular involving its missile program – in return for cash to keep afloat, he adds.

That concern is what stands behind President Bush's focus on keeping weapons of mass destruction out of the wrong hands, says the Naval War College's Mr. Pollack. "Bush has said since at least the 2002 national security estimate that there is no higher priority than preventing a so-called rogue regime from developing such weapons – or acquiring one," he says.

Still, Pyongyang-as-proliferator, though worrying, is a long-term problem – while the likelihood that a nuclear test will set off an Asian arms race is more immediate, experts say.

North Korea gave no hint of when it planned to conduct a nuclear test, leading some experts to suggest that it may be a bluff to draw international attention. But just the threat may be enough to set off a chain reaction in the region, others note.

"The most serious impact would be what this would be likely to cause in the region, prompting other countries to reverse their nuclear nonproliferation policies," says Kimball. In that sense, the North Korea issue parallels the challenge of Iran's nuclear program, since many experts believe a nuclear Iran would tempt other Middle Eastern nations to "go nuclear."

Even now, just because North Korea is threatening to test a nuclear weapon, Japan may well do away with Article Nine of the post-World War II "peace" constitution that bans Japan from sending its "self-defense" forces to fight foreign wars.

If North Korea goes through with a test, Japanese scientists are likely to complete the process of building nuclear weapons. Kim, the Korean defense analyst, estimates that Japan could become a nuclear power within months, despite its aversion to any form of nuclear warfare carried over from the bombing of Hiroshima and Nagasaki.

Such eventualities explain why some experts insist that the real impact of North Korea's test threat would be on global nonproliferation efforts.

"The real challenges are yet to come," says Pollack. "We have to ask if the fact of a North Korea test triggers other responses that fundamentally mean that the nonproliferation regime as we know it has ceased to exist."

• Staff writer Ben Arnoldy contributed to this report.