The Justice Department placed new restraints on federal prosecutors conducting corporate investigations yesterday, easing tactics adopted in the wake of the Enron collapse.

The changes were outlined in a memorandum written by Paul J. McNulty, the deputy attorney general. Under the revisions, federal prosecutors will no longer have blanket authority to ask routinely that a company under investigation waive the confidentiality of its legal communications or risk being indicted. Instead, they will need written approval for waivers from the deputy attorney general, and can make such requests only rarely.

The new guidelines will help companies defend themselves by “making it easier for corporations to say no, and not having to worry about that decision being held against them,” said Andrew Weissmann, who headed the Justice Department’s Enron task force and is now in private practice.

Another substantial change introduced yesterday prohibits prosecutors from considering, when weighing whether to seek the indictment of a company, whether it is paying the legal fees of an employee caught up in the inquiry.