WASHINGTON - Queen Elizabeth II paid tribute to American troops yesterday with a trip to the National World War II Memorial, winding up her six-day U.S. visit.

Joined 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. troops who died in the war.

The queen then joined a park ranger for a walk around a fountain at the center of the memorial before veterans of the war, some in wheelchairs.

One veteran, Marjorie Gallun, 85, told the queen: "We are happy to have you here."

The queen replied: "We are happy to be here."

The queen, a teenage princess during the war, served her country then as a driver in the Women's Auxiliary Territorial Service, the women's branch of the British army.

She was concluding her Washington visit by hosting a dinner for President and Laura Bush at the British Embassy last night - a return favor for the state dinner Monday.

The queen yesterday also toured NASA's Goddard Space Flight Center in Maryland, where, by video link, she heard three astronauts describe their work aboard the International Space Station.

Earlier, Laura Bush joined the queen and Prince Philip in visiting the Children's National Medical Center, where the queen spoke to ill children, who were making cookies.

The royals were flying back to England last night.