OAKWOOD VILLAGE, Ohio — As a group of prominent black pastors listened , the top federal prosecutor in northern Ohio, Justin E. Herdman, spoke recently at Mount Zion church about the prospect that a gunman could target one of their congregations.

The subtext was clear. Mr. Herdman is among a group of federal law enforcement officials who have begun speaking more forthrightly about fighting domestic terrorism from the front lines. They want to reassure a skeptical public that the Justice Department is forcefully combating racist and politically motivated violence in the Trump era, amid their own mounting concerns about a possible surge in attacks sparked by the 2020 election.

“When I sit in church,” Mr. Herdman told the pastors, “I have one eye on what’s going on at the altar, and I have got one eye on the entrance to the sanctuary.”

“Mm-hmm,” the pastors responded in unison.

The community relations effort is the most visible of several aggressive steps by federal prosecutors and F.B.I. agents to combat domestic terrorism. The bureau has about 850 open investigations across the United States. Prosecutors have backed rewriting the laws on domestic terrorism. And in northern Ohio, Mr. Herdman has encouraged his investigators to use wiretaps, one of their most intrusive tools, in such cases.