WASHINGTON — Queen Elizabeth II heard three astronauts describe their work aboard the international space station yesterday as she neared the end of a whirlwind, six-day tour of America.

The crewmembers — American Suni Williams and two Russians, Commander Fyodor Yurchikhin and Flight Engineer Oleg Kotov — answered questions from British-born NASA astronaut C. Michael Foale, who stood next to the queen. The video link at the Goddard Space Flight Center was one-way, so the crewmembers could not see the queen standing by silently wearing a large yellow hat.

After hearing from the astronauts, the British royal continued a tour of Goddard, in suburban Greenbelt, Md. She helped plant a tree in a garden outside the flight center commemorating her visit. The flight center is home to the largest organization of scientists and engineers in America, according to NASA.

Later in the day, the queen paid tribute to American soldiers with a trip to the National World War II memorial before capping her visit by hosting a dinner for President Bush and his wife, Laura, at the British Embassy. It was a return favor for the white-tie state dinner Mr. Bush put on for the royal couple Monday night at the White House.

The queen, accompanied by her husband Prince Philip, had a full day of sightseeing in the U.S. capital planned for yesterday, including a stop at the Children’s National Medical Center with the first lady.

It was to be the British Monarch’s first visit to the war memorial, which was dedicated in 2004. The queen, a teenage princess during World War II, won permission in 1945 from her father, King George VI, to join the war effort as a driver in the Women’s Auxiliary Territorial Service, the women’s branch of the British Army. She became known as no. 230873 Second Subaltern Elizabeth Windsor.

The royal couple will fly back to England last night.

On Monday morning, the Bushes waited on a near-perfect spring day as the queen and Prince Philip arrived by limousine for their official welcome at the White House. The two couples briefly shook hands before moving on to the formal welcome, which included trumpet fanfares and a 21-gun salute.

The day ended with a second visit to the White House for the administration’s first white-tie state dinner. It was designed to showcase American culture and cuisine. But the hosts did not forget to include special touches designed to honor its British ally and make the queen feel welcome.

The centuries-old vermeil flatware and candelabras came from a London silversmith. A made-of-sugar replica of the queen’s 1953 coronation rose graced the cake.