The new rules will also relax a restriction on administering lie-detector tests and searching people’s trash. Under current rules, agents cannot use such techniques until they open a “preliminary investigation,” which — unlike an assessment — requires a factual basis for suspecting someone of wrongdoing. But soon agents will be allowed to use those techniques for one kind of assessment, too: when they are evaluating a target as a potential informant.

Agents have asked for that power in part because they want the ability to use information found in a subject’s trash to put pressure on that person to assist the government in the investigation of others. But Ms. Caproni said information gathered that way could also be useful for other reasons, like determining whether the subject might pose a threat to agents.

The new manual will also remove a limitation on the use of surveillance squads, which are trained to surreptitiously follow targets. Under current rules, the squads can be used only once during an assessment, but the new rules will allow agents to use them repeatedly. Ms. Caproni said restrictions on the duration of physical surveillance would still apply, and argued that because of limited resources, supervisors would use the squads only rarely during such a low-level investigation.

The revisions also clarify what constitutes “undisclosed participation” in an organization by an F.B.I. agent or informant, which is subject to special rules — most of which have not been made public. The new manual says an agent or an informant may surreptitiously attend up to five meetings of a group before those rules would apply — unless the goal is to join the group, in which case the rules apply immediately.

At least one change would tighten, rather than relax, the rules. Currently, a special agent in charge of a field office can delegate the authority to approve sending an informant to a religious service. The new manual will require such officials to handle those decisions personally.

In addition, the manual clarifies a description of what qualifies as a “sensitive investigative matter” — investigations, at any level, that require greater oversight from supervisors because they involve public officials, members of the news media or academic scholars.