China stirred widespread speculation this week with the disclosure that it had moved regular army troops into new positions along its border with North Korea. Press reports from Hong Kong said as many as 150,000 troops were involved. China quickly denied any buildup of troop numbers, but it did say that it was replacing armed police with military troops “in a reform of border administration.”

Why the change? The Washington Post quoted unnamed analysts as saying that the unusual Chinese comment on a military matter could be aimed at stepping up pressure on North Korea to abandon its nuclear weapons program.

A more likely explanation involves China’s continuing problem of 10,000 to 20,000 North Korean refugees said by human rights organizations to be fleeing into China every week to escape famine and political repression. An estimated 300,000 are already there.

The United States encourages this refugee flight and has urged China to accept even more of them as pressure and an embarrassment for North Korea. China has refused to accept this burden and often rounds up refugees and sends them back to North Korea. More important, China fears a far greater influx of refugees if war should break out between the United States and North Korea.

So China may be sending a message to Washington more than to Pyongyang. Bush administration officials interpret China’s brokering of U.S.-North Korean negotiations (in talks that also included South Korea, China, Russia and Japan) as intended to persuade North Korea to halt and dismantle its nuclear weapons program.

Partly so. China does, indeed, fear that a nuclear North Korea could trigger a nuclear arms race in East Asia or even a major war. But it also must fear a possible U.S. armed strike against weapons plants in North Korea. China’s primary stated goal in the area is a reduction of armed forces, including those of the United States, and a denuclearized Korean peninsula.