In the days before the Jan. 6 rally, local and federal officials took a different tack in their preparations.

Ms. Bowser, in a letter to federal officials Monday, urged a light security footprint for Wednesday’s protests to avoid the type of show of force that inflamed tensions during last year’s racial-justice protests.

Military and defense officials offered assistance and prepared what all sides saw as a sufficient number of D.C. National Guard soldiers—about 340—to perform support duties such as traffic management, military officials said.

The U.S. Capitol Police, which is responsible for security at the Capitol and answers to Congress, twice told the Pentagon that no additional support was needed, according to officials and a Defense Department timeline. Local police generally require permission from Capitol Police to control crowds on the grounds of congressional buildings.

“The general attitude from Capitol Police was: ‘We got this. We do this all time,’” said a U.S. official familiar with the discussions.