BEJIING—The escalating crisis on the Korean peninsula is upsetting a delicate nuclear balance between China and the U.S. and exposing a serious flaw in their relationship: the absence of a regular military dialogue on nuclear arms.

The message John Kerry brings to China on Saturday on his first visit as secretary of state is that the U.S. plans to boost its missile defenses in Alaska and Guam are directed at Pyongyang, rather than Beijing, but that it is now in China's own security interests to rein in North Korea.

While U.S. officials hope the deployments will help bring China around to this view, the risk is that China will instead expand plans already under way to strengthen its nuclear arsenal, prompting similar reactions from others in the region. That—to a greater extent even than North Korea's actions—could add a dangerous nuclear dimension to a conventional arms race in Asia.

Exacerbating the problem, analysts say, is the lack of a regular China-U.S. nuclear-security dialogue to build trust and understanding about each other's nuclear forces and strategy, such as the one Washington and Moscow have had since the Cold War, which helped avoid miscalculations and ultimately led to pacts to reduce and share information about their nuclear arsenals.

The dynamics are different because China and the U.S. have deeply entrenched economic ties, and because China's military capabilities still lag far behind those of the U.S. Nor does the Cold War provide a positive model for Beijing and Washington.