WASHINGTON - The six-story tan brick building on H Street houses one of the most secret museums in Washington.

It's not listed in visitor guides, and if any camera-toting tourists should show up, they won't get past the front door or the reception desk behind the bulletproof glass.

This is the headquarters of the Secret Service, the federal agency charged with protecting the life of the president and battling financial fraud. On the first floor, not far from the front lobby, is the agency's museum. It is, unsurprisingly, closed to the public.

The museum, no bigger than a few hundred square feet, is open only to the Secret Service's 6,000 employees and to official visitors. An occasional academic is admitted, said Special Agent Malcolm DuBois Wiley Sr., a spokesman for the agency.

Its collection, including items from assassination attempts, is unlike anything at the Smithsonian or the National Archives.

The window from the limousine that was carrying President Ronald Reagan when John Hinckley Jr. shot him in 1981 is on display, bearing a bullet hole.

"Here's the standard-issue tommy gun that was used until 1960," noted the museum's archivist, pointing to the submachine gun on the wall. The archivist strolled through the displays, occasionally noting interesting items. The museum, at the moment, had no other visitors.

The archivist is a middle-age man who wears trim suits with white shirts and speaks in hushed tones. Under Secret Service policy, his identity is secret. He watches over a remarkable collection of tools and artifacts used by the Secret Service and its opponents.

Along one wall, the museum honors the 35 men and women who died in the line of duty since the agency was founded in 1865. At the building entrance, employees are reminded of the service's iconic motto: "Worthy of trust and confidence."

Besides guarding the president, his family, and other officials and visiting dignitaries, the Secret Service fights various types of financial fraud and the counterfeiting of U.S. currency.

"This is the printing press used by Count Victor Lustig," the archivist said. Lustig was a confidence man who worked with engraver William Watts to flood New York with phony $100 bills during the Great Depression.

"King of counterfeiters" William Brockway and other masters of the craft also have displays in the museum.

Phony $100 bills from different eras line the walls. They are posted next to legitimate bills, along with magnifying glasses for comparing them.

Missing from the phony money are the fine engraving lines and embossing that are on legitimate bills. Sometimes the color scheme is wrong or the Benjamin Franklin doesn't look quite as sharp as he does on legitimate bills.

On an upper floor, there are several wall displays with millions of dollars worth of currency that no longer circulates, including the $500, $1,000, and $10,000 notes. There is also a rare $100,000 gold certificate, which was used in transactions between the Treasury and the Federal Reserve during the Depression.

The displays are behind locked doors in an area that houses the Secret Service's forensic scientists and currency experts, who trace the origins of counterfeit bills. They may be some of the world's best counterfeiters as well.

"We counterfeit new currency before it comes out," an official said. "We want to assess how difficult it is to counterfeit with common printing and art supplies."

As with nearly everyone in the building, the official's identity could not be divulged.