A federal appeals court in California is expected to rule soon on whether states can force firearm manufacturers to incorporate safety devices in their products, a development that could have broad effect on whether and how quickly President Barack Obama’s recent calls for more “smart guns” takes effect.

The Ninth U.S. Circuit Court of Appeals in San Francisco, which covers a wide swath of the West, is weighing a challenge to a California law requiring manufacturers to make handguns that won’t fire a bullet left in the chamber...