The Obama administration oversaw around nine or 10 leak-related prosecutions, depending on how they are counted. That was more than all previous presidents combined, although two of them were investigations inherited from the Bush-era task force. And Mr. Trump has encouraged taking an even harder line.

In February, Mr. Trump told Mr. Comey, then the F.B.I. director, that the bureau should consider prosecuting reporters for publishing classified information, according to a contemporaneous memo Mr. Comey wrote about the conversation. The government has never charged a reporter for publishing restricted information, and Mr. Sessions on Friday did not respond to a question about whether such a step was under consideration.

Speaking to reporters in a subsequent briefing, Mr. Sessions’s deputy, Rod J. Rosenstein, demurred when asked whether the administration would prosecute reporters in relation to leaks, saying he would not “comment on hypotheticals.” He also said the review of the leak investigation guidelines had just begun and it was not clear what, if anything, would be changed about them.

The department’s rules require investigators to exhaust all other ways to obtain the information they are seeking before examining reporters’ phone logs or subpoenaing journalists for notes or testimony that could force them to help investigators identify their confidential sources, or face imprisonment for contempt. F.B.I. agents have long chafed under that restriction, which can slow their investigations but is intended to limit any chilling effect on the news gathering process.

In 2013, after a backlash in Congress and the news media over aggressive tactics to go after reporters’ information in leak investigations, Attorney General Eric H. Holder Jr. decided to revise those rules to further tighten limits on when the government is allowed to subpoena telephone companies for logs of a reporter’s phone calls, which could reveal their confidential sources. The changes made it harder for law enforcement officials to obtain such logs without providing advance notice and giving news organizations a chance to contest the request in court.

The tripling of open investigations since January, Mr. Sessions indicated, was driven by a surge in complaints by security agencies about unauthorized disclosures of classified information. He said that during the first six months of the Trump administration, the Justice Department received nearly as many criminal referrals as it did during the three previous years combined.

Two problems complicated assessments of those ratios. First, the department declined to disclose specific figures for the number of such referrals and open investigations. Moreover, its method of tracking such numbers conflates leaks to the news media with other types of unauthorized disclosures, like spying for a foreign power. It was not clear whether the ratios would shift if only leaks to journalists were considered.