North Korea's nuclear program hard to gauge

WASHINGTON -- North Korea is widely recognized as being years away from perfecting the technology to back up its bold threats of a pre-emptive strike on America. But some nuclear experts say it might have the know-how to fire a nuclear-tipped missile at South Korea and Japan, which host U.S. military bases.

If true, it is still unlikely the North would launch such an attack because the retaliation would be devastating.

Amid continuing tensions, a senior U.S. defense official says the Pentagon has delayed an intercontinental ballistic missile test for this week at Vandenberg Air Force Base in California because of concerns the launch could be misinterpreted and exacerbate the crisis.

No one can tell with any certainty how much technological progress North Korea has made, aside from perhaps a few people close to its secretive leadership.

The North's third nuclear test on Feb. 12, which prompted the toughest UN Security Council penalties yet, is presumed to have advanced its ability to miniaturize a nuclear device.

Experts say it's easier to design a nuclear warhead that works on a shorter-range missile than one for an intercontinental missile that could target the United States.

The assessment of David Albright at the Institute for Science and International Security think tank is that North Korea has the capability to mount a warhead on its Nodong missile, which has a range of 800 miles and could hit in South Korea and most of Japan. He said in his analysis, published after the latest nuclear test, that it is an uncertain estimate, and the warhead's reliability remains unclear.

Albright contends the experience of Pakistan could serve as a precedent.

Pakistan bought the Nodong from North Korea after its first flight test in 1993, then adapted and produced it for its own use. Pakistan, which conducted its first nuclear test in 1998, is said to have taken less than 10 years to miniaturize a warhead before that test, Albright said.

North Korea also obtained technology from the trafficking network of A.Q. Khan, a disgraced pioneer of Pakistan's nuclear program, acquiring centrifuges for enriching uranium. The Congressional Research Service says Khan may also have supplied a Chinese-origin nuclear weapon design he provided to Libya and Iran, which could have helped the North in developing a warhead for a ballistic missile.

But Siegfried Hecker at Stanford University's Center for International Security and Cooperation, who has visited North Korea seven times and been granted unusual access to its nuclear facilities, is skeptical the North has advanced that far in nuclear device miniaturization.

"Nobody outside of a small elite in North Korea knows -- and even they don't know for sure," he said in an emailed response to questions from The Associated Press. "I agree that we cannot rule it out for one of their shorter-range missiles, but we simply don't know."

"Thanks to A.Q. Khan, they almost certainly have designs for such a device that could fit on some of their short- or medium-range missiles," said Hecker, who last visited the North in November 2010. "But it is a long way from having a design and having confidence that you can put a warhead on a missile and have it survive the thermal and mechanical stresses during launch and along its entire trajectory."

The differing opinions underscore a fundamental problem in assessing a country as isolated as North Korea, particularly its weapons programs: Solid proof is very hard to come by.

In an interview Friday, Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, said the United States does not know whether North Korea has "weaponized" its nuclear capability.

Still, Washington is taking the North's threats seriously.

This past week, the United States said two of the Navy's missile-defense ships were positioned closer to the Korean peninsula, and a land-based system is being deployed for the Pacific territory of Guam. The Pentagon last month announced longer-term plans to beef up its U.S.-based missile defenses.