Senior Justice Department officials are not generally known for public bluster or bold pronouncements, but this October in particular they are under explicit instructions to stay mostly quiet, in the hopes of avoiding the sort of political firestorms that engulfed the department in the last two presidential elections.

The department has instituted what many insiders privately refer to as a “30-day rule,” intended to greatly diminish the number of public appearances or statements by its top officials. An internal Justice Department memo issued this summer and reviewed by The New York Times said senior officials “must be vigilant to prevent the appearance that any of our official duties are an effort to influence the outcome of the election.”

In some ways, the memo reflects Attorney General Merrick B. Garland’s intent to steer well clear of partisanship amid a high-stakes presidential contest in which the Republican nominee, former President Donald J. Trump, faces criminal charges in two federal cases that could evaporate if he wins, or send him to trial if he loses.

For his part, Mr. Trump has no such qualms. He declared on Thursday that if elected, he intends to fire the special counsel Jack Smith on his first day back in office.

“I would fire him within two seconds,” Mr. Trump said in an interview with the conservative radio host Hugh Hewitt.

In stark contrast to such campaign rhetoric, the Justice Department memo underscores the broader concern internally that anything it does or says in the final days of the campaign could be used as political ammunition, particularly since its practices and policies have come under far greater scrutiny since the 2016 election.