Washington  - It's known as "America's attic," but the Smithsonian Institution's National Museum of American History in Washington has shed its dusty image.

A two-year, 85-million-dollar renovation of the museum has flooded its atrium with light in a vast space that on Wednesday hosted US President George W Bush for a rededication ceremony.

"This building is home to many of our national treasures. It is a reminder of our country's proud heritage," said Bush, who himself will soon become part of history as he prepares to leave office. "And today, we're witnessing the beginning of an exciting new era in its history, and I would urge all our citizens who come to Washington, DC, come to this fantastic place of learning."

The museum's most hallowed treasure is the Star-Spangled Banner, the 15-stripe, 15-star, battered US flag that was immortalized into the National Anthem by poet Francis Scott Key in 1814 after it flew during a naval bombardment by British forces of a fort in Baltimore, Maryland.

"Today, nearly two centuries after they were composed, his words are written on the heart of every American and written into the law as our country's national anthem," Bush said.

"And the flag that inspired them is preserved here, thanks to the generosity of some fine citizens, to remind us of the sacrifices that have been made to ensure our freedom."

The flag had nearly been loved to death - hanging for a time on display outdoors and having bits clipped off as souvenirs over the years - and was practically in tatters before a recently completed, 10-year restoration effort.

"We will do whatever it takes to preserve this flag yet again," Smithsonian Secretary G Wayne Clough said.

The 9-metre by 10-metre banner is now housed in a state-of-the art glass case under dim light, and is placed at an angle that allows it to be easily viewed without straining its fabric.

The lighting itself also gives visitors a look at the banner that is similar to the early morning view of the flag still flying that inspired Key's song, which begins "O say can you see, by the dawn's early light."

For a short time after the museum's formal reopening to the public on Friday, visitors can also view a handwritten copy of Abraham Lincoln's Gettysburg Address, delivered to commemorate that Civil War battle and among the most famous speeches in US history. The 272-word speech, written in long hand on several white, lined pages is on loan from the White House through January 4.

Among its other national treasures, which historian David McCullough says fascinate because they are "all the real thing," are the ruby slippers from the Oscar-winning 1939 film The Wizard of Oz, Thomas Jefferson's writing desk and the lunch counter where a group of black students staged a sit-in to protest racial segregation in the US South in 1960.

But not everything in the museum is history; on Wednesday part of the focus was on the present as five immigrants took an oath to become US citizens.

There was also a little bit of the future. A chronology of US presidents includes a picture of Barack Obama, who will be sworn in as the 44th president on January 20.