During a visit to South Korea, Secretary of Defense Robert Gates inadvertently underscored a major flaw in Washington’s policy regarding North Korea. Speaking in Seoul, Gates stated that North Korea posed a serious threat to America’s allies in northeast Asia (Japan and South Korea) and pledged that the United States would “continue to provide extended deterrence, using the full range of military capabilities, including the nuclear umbrella” to protect those countries.

Making a public pledge to shield Japan and South Korea with America’s nuclear umbrella was unwise on two counts. First, it eliminates the principal incentive for Beijing to regard North Korea’s nuclear weapons program as a serious problem for China, not just the United States and its allies. As columnist Charles Krauthammer aptly put it when the current crisis began in late 2002, America’s nightmare is a nuclear-armed North Korea, but China’s nightmare is a nuclear-armed Japan.

By reiterating Washington’s commitment to extended deterrence — especially the nuclear component — U.S. officials send a message to Chinese leaders that they don’t need to worry about Japan (or South Korea) developing an independent deterrent. In fairness to Gates, he was not the first U.S. official to make that blunder. After North Korea’s first nuclear test, Secretary of State Condoleezza Rice issued a similar, highly public pledge.

Apparently U.S. leaders don’t know even the basics about playing international diplomatic chess. Obligingly eliminating the specter of a nuclear-arms race in northeast Asia is akin to casually surrendering one’s queen in a chess match with Chinese officials. Granted, the United States might want to discourage Tokyo and Seoul from building their own nuclear arsenals, thereby exacerbating the global proliferation problem, but it is unwise to make high-profile public statements to that effect. Any continuing commitment to extended deterrence should be confined to quiet, private assurances to Japanese and South Korean leaders.

Washington’s public statements, as well as private discussions with the Chinese, need to adopt a totally different tone: that a nuclear-armed North Korea changes the entire strategic equation in northeast Asia, and that the United States cannot possibly guarantee that Japan and South Korea will not decide at some point that their own security needs dictate building independent deterrents. That is the one development that might prod Beijing into getting far tougher with North Korea on the nuclear issue.

The fawning U.S. promises to persist with extended deterrence not only play into the hands of Chinese leaders who want to avoid taking a hard-line toward Pyongyang, it plays into the hands of security free riders in Japan and South Korea. For decades, those two countries have woefully under-invested in their own defenses. Even as Japanese and South Korean leaders insist that North Korea poses a serious threat, they persist with anemic defense budgets. Although it shares a border with perhaps the most ruthless and unpredictable country in the world, South Korea spends less than 2.5 percent of its gross domestic product on the military. Seoul continues to rely on the United States for critical elements of its defense, especially air and naval power.

Security free riding is also alive and well in Japan. Indeed, South Korea’s military effort seems robust compared to Japan’s. Despite North Korea’s repeated saber-rattling, Tokyo spends a paltry 0.9 percent of its GDP on defense, and that situation may get even worse under the new left-leaning government.

U.S. officials who make repeated pledges to continue extended deterrence are enablers of such irresponsible behavior on the part of Washington’s northeast Asian allies. Not only do such pledges discourage Japan and South Korea from building independent nuclear capabilities, it allows them to refrain even from taking prudent measures to build more robust conventional capabilities. It is just too easy for them to rely on the United States to take care of North Korea or any other security threats that might emerge.

Secretary Gates did both America and the nations of northeast Asia a disservice with his comments in Seoul. His statements, and the policies they represent, may make the North Korean nuclear problem even more dangerous than it is already.