Washington ? North Korea’s knock on the door of the burgeoning nuclear club has thrown into question the decades-old idea of a nuclear elite pledged to keeping other countries out.

Now grave concerns are being raised not only over that country’s potential ascension into the ranks of nuclear powers but also about whether North Korea will spread the technology.

North Korea admitted this month that it has flouted a 1994 agreement to freeze nuclear weapons development. The revelation adds to growing worries on nuclear tensions between India and Pakistan and efforts by countries such as Iraq to develop the ultimate weapon.

An abundance of nuclear technology in North Korea, long known for its ballistic missile sales, anticipates a nightmare domino effect, experts say. That argument is underscored by the likelihood that recent club member Pakistan, despite its denials, helped the reclusive east Asian dictatorship to the door.

“The concern is North Korea becoming a nuclear Kmart, complete with blue-light specials,” said Jon Wolfsthal, a nuclear proliferation expert at the Carnegie Endowment for International Peace.

The nonproliferation treaty of 1968 was aimed at confining nuclear weapons to the United States, Russia, Britain, France and China and coming up with formulas for those nations to eliminate their weapons systems. The treaty suffered its first major blow in 1998.

Stirred by clashes in the disputed Kashmir province, India and Pakistan openly tested weapons they had previously refused to acknowledge having. The United States reined in passions with the quick threat of punishment, but experts say the Indian subcontinent is the likeliest site of the first belligerent use of nuclear weapons since 1945.

Long-term danger

By contrast, experts believe North Korea’s short-term priority is simply to deter South Korea and its allies from seeking the downfall of Kim Jong Il’s government.

The longer-term danger is reflected in North Korea’s propensity for selling long-range ballistic missile technology to all takers, with intelligence agencies tracking deals with Iran, Syria and Iraq.

Such missiles now in those hands already pose threats to Western interests in the Middle East. Armed with nuclear warheads, they could change the world balance of power forever.

“North Korea says it sells ballistic missile technology because it’s in dire straits; it needs cash,” said Steve LaMontagne of the Center for Arms Control and Non-Proliferation. “What if it takes the same attitude with nuclear technology, selling it to other countries or even terrorists?”

That depends on how far along the weapons program is.

How many, how far?

The United States long has thought North Korea had a bomb or two manufactured from plutonium. Another cache of fuel rods sealed by the United States after the 1994 pact might have produced five more.

Even at that level, there would have been few implications beyond the balance of power on the Korean peninsula.

“Two, four, even eight warheads that would make them feel secure and deter the United States,” Wolfsthal said, and not much more. “The huge problem would be a surplus of nuclear materials.”

That danger emerged this summer when the United States uncovered evidence of purchase orders for materials aimed at building centrifuges to separate weapons-grade uranium from lower-grade uranium. Uranium is easier to hide and more reliable than plutonium.

“If you have a supplier and a buyer out there, it’s a matter of time until they hook up,” said Stephen Blank, a Koreas expert.