WASHINGTON — National Archives visitors know they'll find the Declaration of Independence, the U.S. Constitution and the Bill of Rights in the main building's magnificent rotunda in Washington. But they won't find the patent file for the Wright Brothers' flying machine or the maps for the first atomic bomb missions anywhere in the Archives inventory.

Many historical items the Archives once possessed are missing, including:

Civil War telegrams from Abraham Lincoln.

Original signatures of Andrew Jackson.

Presidential portraits of Franklin Delano Roosevelt.

NASA photographs from space and on the moon.

Presidential pardons.

Some were stolen by researchers or Archives employees. Others simply disappeared without a trace.

And there's more gone from the nation's record keeper.

The Archives' inspector general, Paul Brachfeld, is conducting a criminal investigation into a missing external hard drive with copies of sensitive records from the Clinton administration. On the hard drive were Social Security numbers, including one for one of former Vice President Al Gore's daughters.

Because the equipment also may include classified information, Sen. Charles Grassley, R-Iowa, calls it a major national security breach.

Brachfeld has documented thousands of electronic storage devices, including computers and servers, that have gone missing over the past decade from the National Archives and Records Administration.

Grassley, who has demanded an accounting of all missing items, said the loss of historical documents "robs our nation of its history and is completely unacceptable."

The Archives' stewardship of the nation's records has been questioned before. In a well-publicized incident, former President Bill Clinton's national security adviser, Sandy Berger, took documents from the Archives in the fall of 2003 while preparing, along with other ex-Clinton administration officials, for testimony to the Sept. 11 commission.

In September 2005, Berger was sentenced to two years of probation, 100 hours of community service, a $50,000 fine and loss of his security clearance for three years.

Some records have been missing for decades from the Archives' 44 facilities in 20 states and the capital, including 13 presidential libraries.

"When I came here nine years ago, there was no acknowledgment that we had a problem," Brachfeld said in an interview with The Associated Press.

Since then, he has started a recovery team that attends trade shows and Civil War re-enactments, and enlists the help of dealers and researchers to recover historical items that belong to the government.