The Korean Mouse That Roared

THERE is something surreal about North Korea as a nuclear menace. This Stalinist Jurassic Park, an economic basket case living on its own propaganda, should by rights be ignored. But Pyongyang has parlayed sheer audacity into crisis politics, confronting the United States and demanding concessions.

Violating the rules of the international nuclear inspection system and threatening to leave it altogether has already gained Pyongyang down payment on billions of dollars in prospective aid. And it keeps trying to unite the Korean peninsula on its terms. Talk about The Mouse That Roared. Unfortunately, this mouse has poison teeth and must be taken seriously.

Playing the nuclear card inflates North Korea's importance. But it also has an army nearly a million and a half strong. Some 80,000 men are stationed in jumpoff positions just north of the 2 1/2 mile wide demilitarized zone. Seoul, South Korea's capital, lies only 25 miles south of the DMZ. Anyone who has seen the invasion tunnels that Pyongyang has dug under the DMZ has no doubt that the threat is real.

The test of will between the United States and North Korea has two aspects. One is the security of South Korea, which the United States is bound to protect not only by treaty but also because of its link with the security of Japan. The second is the emergence of North Korea as a rogue nuclear state, cutting across the international convention against the proliferation of nuclear weapons. Washington worked hard to reach an agreement, concluded Oct. 21, 1994, which freezes and then dismantles the North's nuclear program in return for two much less dangerous light-water reactors for electric power. It leads also to normal diplomatic, trade, and aid relations between them.

In the torturous negotiation of the agreement, it was clearly understood that the reactors would be supplied by South Korea, which is providing half the roughly $4.5 billion involved. A supply contract, setting down the practicalities of the diplomatic accord, is to be signed by tomorrow. But Pyongyang refuses to accept South Korean reactors and the technical help to install them (American reactors would be ''all right'') and has turned April 21, originally a target date, into a deadline.

It hints that if the date passes, its now-frozen nuclear installations would be reactivated. The United States has warned that such a move would bring United Nations economic sanctions. North Korea retorts that sanctions would be tantamount to a declaration of war.

North Korea is not a nuclear power in the accepted sense but it is a powerful nuclear nuisance. While having no nuclear weapon, it does apparently have enough fissile material for two bombs and potentially for five more. This could fetch a high price from Iran, Iraq, and Libya -- indeed, from any country with nuclear ambitions. North Korea has already sold medium-range missiles of its own manufacture. And, if it has no bomb, the bomb materials are valuable enough for terrorism. Plutonium could contaminate a big city's water supply or make parts of the city uninhabitable. North Korea's record of state terrorism suggests that it would have no inhibitions against selling -- or using -- the nuclear means.

For all its brass, North Korea faces a dilemma.

There may be more money, for the longer run, in pursuing cooperation with the US. It is already trying to chisel an additional billion dollars in aid to provide the completely missing infrastructure of a peaceful electric power grid -- lines, pylons, transformers, roads, trucks, etc.

But then comes Pyongyang's other, perhaps primary, objective: to take over South Korea. This was the goal of the 1950 invasion and has been, however unsuccessfully, pursued ever since. Terrorist acts have failed to destabilize South Korea's government. Political pressure has been applied to marginalize and eliminate South Korea as a sovereign partner in the reunification of the peninsula. Pyongyang wants the 1953 armistice replaced by a US-North Korean peace. It has paralyzed the Military Armistice Commission and quietly expelled the two members of the Neutral Nations Supervisory Commission, Poland and Czechoslovakia, on the northern side of the truce line. An ''Agreement on Reconciliation, Nonaggression, Exchange, and Cooperation'' signed in 1991 has remained a dead letter. A later agreement on denuclearization of the peninsula gave up the ghost when North Korea refused to accept challenge inspections. Pyongyang now wants to discuss the future of Korea only with the United States.

Washington says it has no intention of selling out South Korea. What could Pyongyang do to make it? Start another crisis tomorrow and immediately lose the money and the prospect of international respectability now within reach? After years of high-stakes poker with a pair of deuces, North Korea may have something up its sleeve. But it looks as though, whatever quibble or delay it might use to save face, North Korea is running out of bluff.