A seasoned American specialist on North Korea suggests that Pyongyang has acquired the capability to strike South Korea, Japan, and American bases there with nuclear weapons, causing tens of thousands of deaths.

Bruce Bechtol, a former intelligence officer in the Defense Department, says in a carefully researched essay: “The unthinkable and seldom-discussed threat of a nuclear attack is a nightmare scenario not only for the region but for all nation-states that have interests on the Korean peninsula.”

Besides South Korea, Bechtol says likely North Korean targets would include Japan and U.S. military bases in South Korea and Japan. He singled out the ports of Busan, Pohang, and Incheon in South Korea and Okinawa, Sasebo, and Yokohama in Japan. Most have U.S. bases nearby.

After a North Korean nuclear assault, their Chinese and Russia allies would be engaged immediately. Less directly affected would be Taiwan, the self-governing island off the coast of China, and the nations of Southeast Asia.

While this nuclear sword was being examined, President Lee Myung-bak of South Korea was welcomed to the White House and addressed the Congress last week after a new Korea-U.S. trade act had been passed. Of particular interest to people in Honolulu, Mayor Peter Carlisle was visiting Incheon, a sister-city.

Bechtol, a professor at Angelo State University in Texas, focused on North Korea’s ability to deliver nuclear warheads. In response to an e-mailed query about North Korean intentions, he replied: “In my view, the most likely way that Kim Jong-il [North Korea’s dictator] would use a nuclear weapon would be as an act of desperation.”

“The bottom line here is, anyone who claims either A) North Korea does not have the capability, or B) will never use it, is spouting unproven and dangerous analysis,” he asserted.

Kim has for many years been trying to bludgeon the U.S., Japan, and South Korea into acknowledging that North Korea has a right to nuclear weapons and into signing a treaty in which they promised not to attack North Korea. The U.S., Japan, and South Korea have refused so long as North Korea makes nuclear arms.

Bechtol says North Korea has bombers that could carry and drop nuclear bombs. A more likely scenario, he writes, would have North Koreans disguise a merchant ship by flying the flag of another nation, pull into a port, and detonate a nuclear bomb in its hold. North Korea has also developed medium range ballistic missiles.

“A nuclear attack would likely lead to widespread panic and terror,” Bechtol writes in an article published in a Korean defense journal and on the website of the Nautilus Institute, a think tank in San Francisco. South Korea and Japan are modern nations but their medical personnel would be insufficient to handle thousands of wounded people.

A nuclear attack on South Korea or Japan would also kill a great number of foreigners, many of them Americans. The American civilians who live in South Korea and Japan would require the largest non-combatant evacuation ever conducted in U.S. history, Bechtol says.

“Indeed, a North Korean nuclear attack on Japan would strike not only a tragic blow to the country affected, but would likely be successful in causing political turmoil that would create vulnerabilities in the military reactions of the United States, South Korea, and Japan,” Bechtol says.

He says this leads to asking whether a preemptive strike would prevent a North Korean nuclear attack.

That option would involve more than destroying North Korea’s nuclear weapons — even if their locations were known. “It is very likely that the nuclear weapons are dispersed to several places in North Korea,” he writes.

“A preemptive strike would have to be so widespread and large-scale that there is almost no doubt it would cause an all-out war on the Korean peninsula,” Bechtol says, because of North Korea’s capability to strike back with non-nuclear weapons.

He concludes that avoiding a nuclear war in the Korean peninsula should remain a high priority because there will be no winners, only varying degrees of loss. Unhappily, he does not suggest a way to do this.

Neither did specialists on Korea at Stanford University who asserted in a report: “North Korea must not be allowed to think itself immune from meaningful retaliation for provocations, but the allies must also take care not to respond in ways that risk a major escalation of conflict on the peninsula.”

In sum, no one seems yet to have devised a way to stop the North Koreans short of a catastrophic war.