IT'S TRUE that tourists have taken over the Mall, but this is ridiculous. Now they've pitched a tent in the middle of the Museum of American History.

It's a tourist camp scene, circa 1925. Stuck for the night, the family has been fishing, swimming and playing cards. For the kids, an "autocot" nestles snugly in the 1918 Olds touring car parked beside the tent. (The bird droppings on the car are not original, nor authentic, and "road dust" has been applied over a veneer of Vaseline.) Folding chairs surround a collapsible table set with unbreakable dishes. Eventually, the campsite will be folded up and tied to the running boards, and the family will move on.

This is the main attraction of "At Home on the Road: Autocamping, Motels and the Rediscovery of America." It is about our love affair with the car, via the standard two-week paid vacation of the Fifties. Pennants, postcards and things bearing likenesses of Florida alligators tell of how we made the escape to the road, but couldn't get away from ourselves. The highway became a carnival midway, lined with restaurants and amusements, HoJos and "South of the Border."

An exhibit can't come close to the real experience. The more you are familiar with cross-country car trips of days past, the more you will find missing from this show. Where are the Burma Shave signs, the billboards, the songs of the road, not to mention the stickiness of a Stuckey's pecan milkshake spilled on the back seat?

Anyway, happy motoring! As you travel ask us. And clean up the campsite before you go.

AT HOME ON THE ROAD: AUTOCAMPING, MOTELS AND THE REDISCOVERY OF AMERICA -- At the Museum of American History through September 1, 1986.