HURRY ON DOWN to the Interior Department Museum before they fix it. Largely unchanged for more than half a century, the museum's a time tunnel into the era of the Great White Father and the New Deal.

While the museum has a few exhibits on events as recent as 1989's Hurricane Hugo, most of the displays date to 1936, when the gleaming new Interior Building was inaugurated as a symbol of President Franklin D. Roosevelt's determination to lead the nation out of the Great Depression.

It was a time when Washington still was such a small Southern town that one of the museum's National Park Service exhibits refers to the Civil War as "The War Between the States."

Ironies abound in many of the vintage exhibits. Most are amusing but some are flat embarrassing, such as the idealized illustrations that explain how the Bureau of Indian Affairs has opened more and better land to its dependents and is training them to husband it like white people.

There are self-congratulatory exhibits trumpeting the achievements of once-proud agencies that have fallen into desuetude.

The quality of the exhibits ranges from excellent dioramas and top-quality artifacts to arrangements that might not qualify for honorable mention at a high school science fair. There are scores of the original moon rocks: glassy tektites that were ejected from lunar meteorite craters with such force that they escaped the moon's gravity and fell to earth.

There are bounty land certificates issued to John Paul Jones and Baron von Steuben for their service in the Revolution, and others issued to Robert E. Lee and Stonewall Jackson and their Civil War opponents Ulysses S. Grant and William T. Sherman, for their service as comrades in arms during the Mexican War.

It's rather a jumble, but then so is the manifold mission of the Interior Department. And whatever the sum of the museum's parts, the whole is a captivating glimpse of the beginnings of fundamental change in the American government. It was a time when farm agents, engineers, scientists, social workers, Civilian Conservation Corps volunteers and artists went forth from Washington filled with zeal and vision.

"Hi, I'm from the government and I'm here to help you" has become a sardonic catchphrase, but in the '30s the arrival of an Interior Department employee could mean salvation to a farm family or a struggling breadwinner. An air of the innocence and earnestness of those times lingers in the museum.

For the time being. The museum recently came into the charge of Debra Berke, its first professional curator, who hopes to complete the first stage of a revitalization project by January. That's kind of scary, because the place is an Art Deco gem. Happily, the project's in the hands of Washington's Chris White, demonstrably the most original and ingenious museum designer in town.