The National Archives, which necessarily guards most of its exhibits behind glass, has found a way to get things out where people - particularly children - can touch them.

The display of "National Treasures: Land, Water, Minerals," which opened this week in celebration of the centennial of the U.S. Geological Survey, features a "hands-on" section where children are invited to examine and test pieces of the United States.

The young poeple get drawers of unlabeled samples collected by USGS expeditions and clues to help them figure out what they are. A bunch of rocks becomes, with the help of volunteer docents, a collection of minerals; while solving the mystery they presumably will gain some idea of the richness and variety of the physical structure of the country.

Maps are the major stock in trade of USGS, and the almost endless variety of them the agency produces is demonstrated by a case of dozens of the Washington area: contour, soil types, watersheds, vegetation, land use - even water wells. The latter reveals, as every back-country hiker knows, that even the best maps aren't perfect: One visitor found at least two long-established wells missing.

The hands-on exhibit, in the Pennsylvania Avenue lobby, is limited to 10 to 5 Monday through Friday because of staffing problems.

In the other section of the exhibit, in the Constitution Avenue rotunda, a selection of documents shows that the debate over the proper use of our national resources has been going on at least since the Revolution. And the terms of the debate have been similar all along. At the opening of the 19th century, for instance, the citizens of New Orleans were demanding that Uncle Sam tame the Mississippi, while a Spokane editor was complaining that federal interference was complicating the rape of the West.

The rotunda hours are 9 a.m. to 10 p.m. Monday through Saturday and 1 to 10 on Sunday. Both sections of the exhibit will run through October 15. CAPTION: Picture, A PHOTOGRAPH OF "MAMMOTH HOT SPRINGS, "FROM THE EXHIBIT AT THE NATIONAL ARCHIVES.