Accompanied by former President George H.W. Bush, a veteran of the war, and his wife, Barbara, the queen placed a wreath in honor of the 400,000 U.S. soldiers who died. It said: "In memory of the glorious dead."
Afterward there was a drum roll and a bugler played taps.
Dressed in a sharp blue suit and hat, the queen then joined Mary Bomar, the British-born director of the National Park Service, for a walk around a fountain at the center of the memorial. They stopped to look at the Lincoln Memorial and the Washington Monument before greeting veterans of World War II, some in wheelchairs.
One of the veterans, Marjorie Gallun, 85, who said she served in the Marine Corps, told the queen: "We are happy to have you here."
The queen politely replied: "We are happy to be here."
Outside the memorial, there was a crowd of several hundred behind a picket fence, on which two Union Jacks were draped. The crowd applauded as the queen's limousine went by.
It was the British monarch's first visit to the war memorial, which was dedicated in 2004. The queen, a teenage princess during World War II, served her country in the war as a driver in the Women's Auxiliary Territorial Service, the women's branch of the British army.
She was to conclude her Washington visit by hosting a dinner for the Bushes at the British Embassy Tuesday night, a return favor for the white-tie state dinner Bush put on for the royal couple Monday night at the White House.
It was a full day of sightseeing in the U.S. capital. The queen started off with a trip to NASA's Goddard Space Flight Center in suburban Maryland, where she heard three astronauts describe their work aboard the international space station.
The crew members - American Suni Williams and two Russian cosmonauts, Fyodor Yurchikhin and Oleg Kotov - answered questions from British-born NASA astronaut C. Michael Foale, who stood next to the queen at the center.
The video link was one-way, so the crew members could not see the queen standing by silently.