WASHINGTON — President Trump’s motorcade will do an honorary lap around the IndyCar Freedom 250 Grand Prix route in DC Sunday before some of the world’s fastest racecars take to the streets of the nation’s capital, an administration source told The Post Tuesday.

The 1.66-mile track begins and ends at the base of Capitol Hill — giving an iconic backdrop to the first-ever professional motorsports contest inside the nation’s capital.

The route heads toward the White House on the roadway typically used for inaugural parades — before making a sharp curve around the National Archives and crossing the National Mall.

The cars will loop around the Smithsonian Air and Space Museum and the Museum of the American Indian before reaching the finish line.

Trump will be joined by first lady Melania Trump in the viewing stands at the latest sporting event he will preside over to celebrate America’s 250th birthday.

The green flag will wave shortly after 1 p.m. ET, with festivities including military flyovers due to begin at 11:30 a.m.

Sunday’s grand prix follows Trump hosting a UFC card on the White House South Lawn June 14.

Trump’s official armored vehicle, known as the Beast, previously made a ceremonial lap ahead of the Daytona 500 in 2020 and at NASCAR’s Great American Race last year.

The IndyCar event — the brainchild of Transportation Secretary Sean Duffy  — is happening despite initial resistance from congressional Democrats to displaying commercial advertisements on the vehicles.