WASHINGTON — Attorney General Eric H. Holder Jr. on Wednesday eliminated what journalism groups worried could be used as a loophole in the rules governing how and when prosecutors can subpoena journalists.

For most of his time as attorney general, Mr. Holder oversaw a crackdown on government officials who talked to reporters about national security without permission, bringing more charges against people accused of leaking information than all of his predecessors combined. He also approved subpoenas for numerous journalists. But he recently said that the effort went too far at times.

Mr. Holder first began reviewing the news media guidelines in 2013 during heavy criticism after prosecutors seized some telephone records from The Associated Press and labeled a Fox News reporter, James Rosen, a potential criminal co-conspirator for asking about classified information. He announced revisions last February that made it significantly harder, though not impossible, to demand phone records, notes or emails from news organizations.

Last year, Mr. Holder prevented the F.B.I. from portraying a reporter as a co-conspirator as a way to get around a ban on getting search warrants for reporting materials. That rule would have prevented the subpoena in Mr. Rosen’s case. He also made it harder for prosecutors to seize records in secret, as he did in the A.P. case. And he expanded that protection beyond phone records to cover emails and reporting work product, protections that did not exist previously.