WASHINGTON—Four members of China’s military have been indicted by the U.S. government on charges of hacking into Equifax Inc. and plundering sensitive data on nearly 150 million Americans as part of a massive heist that officials said also stole trade secrets from the credit-reporting agency.

In an escalation of U.S. efforts to counter China’s alleged attempts to use cyber theft and other means of technology acquisition to become the world’s dominant economic power, a federal grand jury in Atlanta returned a nine-count indictment...