For the second time in three years, the North Koreans have been caught with their hand in the nuclear cookie jar.

U.S. officials long feared that Pyongyang has at least two nuclear weapons and enough fissile material for perhaps eight more. Now we know it's worse - North Korea isn't just developing nuclear weapons at home, it's proliferating nuclear materials abroad.

In late 2002, Washington discovered that North Korea had been cheating - for at least four years - on its 1994 agreement to freeze its nuclear-weapons program.

Now the latest U.S. intelligence (gleaned from Libya's dismantled nuke program) suggests that Pyongyang sold Tripoli two tons of the uranium hexafluoride gas used in the production of weapons-grade highly enriched uranium.

But we've snapped up all of Libya's processed uranium - so why is this significant?

Well, first, it confirms longstanding suspicions that North Korea has two active nuclear-weapons programs: The original, Soviet-era plutonium-based program that was supposedly capped by the 1994 agreement - and this parallel, uranium-based program, too.

Second, it shows that Pyongyang has already crossed a nuclear Rubicon: It's selling nuclear weapons materials (and, perhaps, technology) abroad. That proven willingness to proliferate is a standing threat to international peace and security.

Third, the rogue regime can probably pump out nuclear material faster than we'd previously believed. Pyongyang, highly paranoid, isn't likely to be selling this stuff abroad at the risk of undermining its own stockpile at home.

The $64,000 question is: Who else has bought North Korean nuclear materials and/or technology? So far, there's no evidence of anyone besides Libya. But the prime suspects are Iran and Syria - both bad boys already have strong ballistic-missile-trading relationships with Pyongyang.

The nightmare scenario, of course, features an impoverished North Korea selling nuclear materials to a terrorist group. That remains unlikely - even for Pyongyang. (That nuke-toting terrorists could come back to bite you.)

The problem is: You just don't know what you don't know, especially when it comes to proliferation. So what to do in the short run?

IAEA: Scientific sleuthing at Tennessee's Oak Ridge National Laboratory concluded (with 90 percent certainty) that Libyan uranium samples didn't come from rogue Pakistani scientist A.Q. Khan's network. By process of elimination, that left North Korea as the likely culprit.

Understandably, some people remain skeptical about the nuclear finger-pointing. (And it's peculiar that Libya hasn't just told us where and how it got the goods . . .)

OK, fine. Answer the skeptics by giving a sample of the Libyan uranium to the U.N.'s International Atomic Energy Agency for independent analysis.

If the IAEA reaches the same conclusion as Oak Ridge, Washington should find it a bit easier to strengthen the flabby resolve of the international community to deal with the North Korean proliferation threat.

Six-Party Talks: There are few good military options for dealing with the North's nuclear program (which is scattered in underground sites across the country). That leaves diplomacy.

Since August 2003, North Korea has attended three rounds of nuclear discussions, involving the U.S., China, Japan, Russia and South Korea. (It passed on a fourth round last fall in hopes of a President Kerry.) Restarting these talks remains the best option for resolving the Korean nuclear issue.

China: Beijing has more influence here than anyone else. In fact, Mao Tse Tung once quipped that North Korea and China are "as close as lips and teeth." But Beijing's efforts to "pressure" Pyongyang into behaving responsibly have been a lot like Chinese opera - lots of noise and arm-waving, with nothing really going on. If China's as committed to nuclear nonproliferation as it claims, it should lean harder on its old ally. Now.

In a nutshell, the news from Libya is that the problem of North Korean nuclear proliferation is even worse than we'd thought. Unfortunately, few outside North Korea know just how much worse it really is.

Peter Brookes is a Heritage Foundation senior fellow. E-mail: [email protected]