WASHINGTON — The Pentagon will spend $1 billion to deploy additional ballistic missile interceptors along the Pacific Coast to counter the growing reach of North Korea’s weapons, a decision accelerated by Pyongyang’s recent belligerence and indications that Kim Jong-un, the North Korean leader, is resisting China’s efforts to restrain him.

The new deployments, announced by Defense Secretary Chuck Hagel on Friday, will increase the number of ground-based interceptors in California and Alaska to 44 from 30 by 2017.

The missiles have a mixed record in testing, hitting dummy targets just 50 percent of the time, but officials said Friday’s announcement was intended not merely to present a credible deterrence to the North’s limited intercontinental ballistic missile arsenal. They said it is also meant to show South Korea and Japan that the United States is willing to commit resources to deterring the North and, at the same time, warn Beijing that it must restrain its ally or face an expanding American military focus on Asia.

“There’s been a quickening pace of provocations,” said one senior administration official, describing actions and words from North Korea and its new leader, Mr. Kim. “But the real accelerant was the fact that the North Koreans seemed more unmoored from their Chinese handlers than even we had feared.”