President Obama will speak from the steps of the Lincoln Memorial on Wednesday, marking the 50th anniversary of Martin Luther King Jr.’s historic “I Have A Dream” address and the March on Washington.

The event will feature appearances by former presidents Bill Clinton and Jimmy Carter; entertainers Oprah Winfrey, Jamie Foxx and Forest Whitaker; and Robby Novak, a 9-year-old YouTube sensation better known as Kid President.

Musical performers will include Christian singer Natalie Grant and country and pop singer LeAnn Rimes. Peter Yarrow and Paul Stookey, who performed at the 1963 March on Washington, will sing on Wednesday, and Congressman John Lewis, a speaker 50 years ago, will also make an appearance.

Lynda Johnson Robb, whose father Lyndon Johnson was vice president at the time of the march, will also speak. The emcees will be actor Hill Harper and broadcast journalist Soledad O’Brien.

Earlier in the day, at 9 a.m., Shiloh Baptist Church will host a prayer ceremony tied to the commemoration. Only ticket holders can attend.

Those attending the ceremony at the Lincoln Memorial must enter the Mall from 17th Street, just north of the World War II Memorial.

Numerous roads in the area will be closed to vehicular and pedestrian traffic from about 3 a.m. to 6:30 p.m. on Wednesday. Those roads include:

■17th Street between Independence Avenue and Constitution Avenue

■23rd Street from Independence Avenue to Constitution Avenue

■Arlington Memorial Bridge

■Daniel French Drive

■Henry Bacon Drive

■Independence Avenue from 15th Street to 23rd Street

■Maine Avenue from 15th Street to Independence Avenue, including Tidal Basin parking lot

■Ohio Drive from Inlet bridge to Parkway Drive, including the A, B and C parking lots

■Parkway Drive from Rock Creek Parkway to Lincoln Memorial Circle

■Rock Creek Parkway from Virginia Avenue to Parkway Drive

Parts of the 9th Street tunnel, F Street, Maine Avenue, the Maine Avenue exit of I-395, the Potomac River Freeway and the Theodore Roosevelt Bridge will also have detours blocking some directions of traffic. Parking will be barred on Constitution Avenue from 17th to 23rd Streets.

The National Park Service has banned items including backpacks, balloons, and coolers from its property, including the Mall, during the event.