For the Bicentennial, Gary Sandburg of Downey, Calif., grew an Uncle Sam type beard and dyed it red, white and blue. Got a lot of laughs all year. Caused a lot of comment. But then it gets to be 1977, and what do you do with a dated beard?

You cut it off and send it to the Smithsonian, that's what.

"This whole project came out of lunch conversations over the years," said Robert M. Vogel, curator of mechanical and civil engineering for the Smithsonian. "Every curator had a collection of oddments that would never make it into any regular show, things that are a little off-color. Or peculiar. Or just obsessive."

That's how the Nation's Attic exhibit came about. It is a small show, with 100 items (there are 15 million in the Smithsonian), and it lasts until Sept. 15. Roger Kennedy, the new director of History and Technology, was a little nervous about the title, because in the old days, when the Smithsonian really was a musty storehouse and not much else, the name had a certain bite to it. But the museum has come a long way, and when S. Dillon Ripley was confronted with the name and said it didn't brother him, that did it.

The phrase is still not universally loved by curators. One reporter once interviewed a distinguished scientist at the museum and, leading off with cheerful small talk, made a breezy crack about the "nation's attic." The distinguished scientist blew a hole clear through the ceiling. It was 20 minutes before he would consent to do the interview.

A. A. Hirsch worked for the water department of Shreveport, La., and he collected worn-out water meters. He liked their simple but ingenious mechanism. He collected over 1,000 of them, but then he decided to move to a smaller place. Where was he going to stash 1,000 old water meters?

The Smithsonian. Where else?

Vogel has a warm spot for A. A. Hirsch. He too likes mechanical gadgets, expecially antique ones. Trained as an architect at the University of Michigan, he kept veering off the track to study power machinery, bridges and tunnels, things whose function was expressed in their design.

"We tend to shroud functional details today," he said. It's gotten so you can't find a screw on a car, it's all covered up some way. I think we're getting further removed than ever from the physical world. People don't know how things work anymore. I used to see guys in the '30s when I was growing up in Baltimore, and they'd have the car engine broken down and would be grinding the valves. Who grinds their own valves anymore? America's losing its know-how."

Vogel's office is crammed with old texts on engineering. He uses a statuesque rolltop desk, and his visitor sits in a great padded Victorian construction worthy of a Thuringian emperor.

You invented an eyeball massager? An aluminum violin? Black false teeth for Plynesians? You know where to send them.

"The only criterion for this show was that the item had to be strange," said Vogel, who organized it along with curator Carl Scheele and rare-book expert Silvio Bedino under assistant exhibits director Benjamin Lawless. "It's a bit tongue-in-cheek, and in fact this gave us some tongue. There were staff people who thought it was beneath our dignity."

Some of the viewers also have a hard time understanding that you are allowed to laugh in a museum. A white-haired woman exploring the mock-up attic space, where the exhibits are casually crammed, pushes the button that sets a whole plaqueful of false teeth chomping in union. She stares at it, grim, baffled.

"Some of these collectors show an extraordinary narrowness and extraordinary depth," added Vogel. "It's a sort of canyon in collectorship."

You take the safety pin collection, the pencil collection, the paper collection, and all those label collections from whiskey barrels, cigar boxes and apple crates: Shown all in one place, they can be impressive, not to say staggering. There is a whole cabinet filled with rows and rows of thimbles. There are snippets of hair from all the presidents up to Pierce, with Sir Walter Scott and Daniel Webster thrown in. There are 54 miniature working pistols and rifles, some only inch-long. There is a stone from the dungeon in Rouen where Joan of Arc was imprisoned.

Vogel collects mechanical devices. He has collected all his life.

"I can't explain it," he said. "It's not genetic. My father was a schoolteacher, and his father was a real estate development, and beyond that I couldn't say. I am also interested in the past. So the two things come together in antique machines."

He has been with the museum since 1957, moving almost directly from college to service to the Smithsonian.

. . . Borman and Lovell's joint toothbrush from space. An iron-latticed tramp cart for wheeling vagrants out of Rockport, Me. A tobacco plug that went to the North Pole with Admiral Peary. A 28-inch amplified ocarina. A pair of size 18 shoes. Hair jewelry. A tiny box with a spike inside for used gum wads. A Swiss army knife with 30 blades. The mummified hoof of a heroic firehorse, who kept running without it. Victorian fly traps. A nose thumber. . . .