WASHINGTON — The Justice Department could broaden its efforts to bring technology giants to heel, going beyond investigating potential antitrust violations to potentially challenge companies like Google and Facebook on multiple fronts, the deputy attorney general, Jeffrey A. Rosen, warned on Monday.
“We do not view antitrust law as a panacea for every problem in the digital world,” Mr. Rosen said during a speech in Washington at an American Bar Association antitrust forum. “We will not ignore any harms caused by online platforms that partially or completely fall outside the antitrust laws.”
The remarks were Mr. Rosen’s most significant on the Justice Department’s broad look at the technology sector, whose largest companies are dominant forces in communications, entertainment, news, advertising and commerce. The department has been engaged in an in-depth antitrust review and is also working with state attorneys general to determine whether companies like Facebook have obtained too much market power.
Mr. Rosen said that law enforcement officials could also use legal tools that touched on areas including privacy, consumer protection and public safety as part of a broader investigation into the role that online platforms play in the lives of consumers. Google, for example, dominates the online advertising market, and its operating system is found in a majority of smartphones around the world.
The department’s efforts echo the White House’s desire to limit the powers of tech companies. President Trump has accused Facebook and Twitter of using their algorithms to hide the speech of conservatives, even as Mr. Trump himself has harnessed those platforms to power his re-election bid, spread conspiracy theories and attack his political enemies.
In response, Facebook executives have courted the White House and conservative politicians as they seek to fend off scrutiny and regulation. Mark Zuckerberg, the chief executive of Facebook, and Sheryl Sandberg, its chief operating officer, have spent time with conservative lawmakers, and Mr. Zuckerberg met with Mr. Trump in the Oval Office this fall.
“There is a growing consensus from the right to the left that antitrust is an important tool, but not a silver bullet, and that broader policy tools will be needed to rein in tech platforms abuses,” said Gene Kimmelman, senior adviser to Public Knowledge, an internet and communications think tank, and a former Justice Department antitrust official.
“My only fear is whether this new appetite for platform oversight may been an effort to influence the content takedown decisions of the platforms going into the elections,” Mr. Kimmelman said.
A Justice Department spokesman declined to comment beyond Mr. Rosen’s remarks.
Attorney General William P. Barr has voiced his concerns that the companies are deploying products that put public safety at risk by stymieing law enforcement, reviving the Justice Department’s yearslong fight for access to popular communications platforms that are increasingly employing strong encryption that is nearly impossible to crack.
That conflict came to a head in 2016 when a federal judge ordered Apple to help the F.B.I. unlock an iPhone used by one of the mass shooters in San Bernardino, Calif. Tensions between the two sides eased after the F.B.I. ultimately opened the device without Apple’s help.
This fall, the Justice Department turned its gaze from Apple to Facebook, which plans to make WhatsApp and its other messaging services more secure. Mr. Barr and his counterparts in Britain and Australia said in a letter to Mr. Zuckerberg that he is wrong to create communications products that they claim essentially shield terrorists and other criminals.
“Companies should not deliberately design their systems to preclude any form of access to content even for preventing or investigating the most serious crimes,” they wrote.
That letter came after Trump administration officials debated whether to seek a law to effectively ban end-to-end and other forms of encryption — a legislative option that is all but dead for now as Congress undertakes a politically charged impeachment inquiry.
Ryan Shores, an antitrust lawyer who joined Mr. Rosen’s office last month as his senior adviser for technology industries, will lead the broader review, Mr. Rosen said. Mr. Shores was initially brought into the department to investigate the competitive conditions among online platforms. Mr. Rosen vowed at the time his hiring was announced to “vigorously seek to remedy any violations of law, if any are found.”
In addition to Mr. Shores, Justice Department leaders are deeply involved in the review of the nation’s technology companies. Mr. Barr worked in the telecommunications industry during the 1990s, serving as general counsel for the telecom company GTE where he argued an antitrust matter before the Supreme Court.
And Mr. Rosen was lead counsel for Netscape Communications, the Web browser that filed the antitrust complaint that ultimately helped to undo Microsoft’s monopoly in search and software.
Cecilia Kang contributed reporting.