When the federal authorities last week seized the phones of top City Hall officials in New York, it was another stunning public move by investigators who had already taken Mayor Eric Adams’s devices, searched his aides’ homes and issued subpoenas to members of the mayor’s staff.

The intensity — and sheer volume — of the federal scrutiny has raised urgent questions about the scope of what federal agents are seeking and how much longer they intend to seek it, especially with the Democratic mayoral primary approaching next year.

A representative of the U.S. attorney’s office for the Southern District of New York, which is conducting most of the investigations, declined to answer questions about the inquiries or say whether the office would issue a statement if no charges were filed, as it has done with other recent investigations.

But interviews with four former federal prosecutors, including two who headed the public corruption unit within the same office that is investigating the Adams administration, said that U.S. investigators would not have taken such significant steps if they did not believe there was sufficient reason for doing so.

The scope of the seizures signals “an intensity of interest” from federal investigators and “a complete distrust of the so-called cooperation” from the city, said Daniel C. Richman, a Columbia Law School professor who worked as a federal prosecutor in Manhattan in the late 1980s and early 1990s. The actions, he said, also point to the “extent of development of the case.”

Across the cases, investigators appeared to be ranging widely through the administration, examining not just the mayor but the heads of the police and the schools and some of Mr. Adam’s top deputies: Agents on Wednesday took the phones of Edward Caban, the police commissioner, as well as the first deputy mayor, the schools chancellor and others. They searched the home of a consultant who is a brother both of the schools chancellor and one of Mr. Adams’s deputy mayors.