Washington ? The National Museum of American History will close for almost two years to reconfigure the core of its often-mystifying layout and build a new gallery for the Star-Spangled Banner.

The 42-year-old museum, the largest history museum in the country and the third-most-visited branch of the Smithsonian, will close Sept. 5, the day after Labor Day, officials announced Wednesday. Construction is expected to be completed by summer 2008.

The museum is home to some of the country’s iconic symbols, such as the desk on which Thomas Jefferson wrote the Declaration of Independence and the top hat Abraham Lincoln was wearing the night of his assassination, as well as cultural curiosities such as the ruby slippers Judy Garland wore as Dorothy in “The Wizard of Oz” and the home kitchen of famed chef Julia Child.