SAN FRANCISCO — A Justice Department official hinted on Monday that a yearslong fight over encrypted communications could become part of a sweeping investigation of big tech companies.

While a department spokesman declined to discuss specifics, a speech Monday by the deputy attorney general, Jeffrey A. Rosen, pointed toward heightened interest in technology called end-to-end encryption, which makes it nearly impossible for law enforcement and spy agencies to get access to people’s digital communications.

Law enforcement and technologists have been arguing over encryption controls for more than two decades. On one side are privacy advocates and tech bosses like Apple’s chief executive, Timothy D. Cook, who believe people should be able to have online communications free of snooping. On the other side are law enforcement and some lawmakers, who believe tough encryption makes it impossible to track child predators, terrorists and other criminals.

Attorney General William P. Barr, joined by his British and Australian counterparts, recently pressed Facebook’s chief executive, Mark Zuckerberg, to abandon plans to embed end-to-end encryption in services like Messenger and Instagram. WhatsApp, which is owned by Facebook, already provides that tougher encryption.