"Cast your eyes upon the greatest thing yet built by human hands," sang Woody Guthrie. "On the King Columbia River it's the big Grand Coulee Dam."

Grand Coulee is impressive, sure, but it is only one dam. Eighteen are represented in "Built for the People of the United States: Fifty Years of TVA Architecture" at the National Building Museum on Judiciary Square.

Considering its subjects -- its huge, man-hollowed mountains, its armies of Tennessee Valley Authority laborers working round the clock, its 800-foot-high smokestacks, its boilers that consume 1,000 tons of coal an hour -- the show should overwhelm. It ought to roar with rushing torrents, hum with whirring turbines and make the spirit soar.

But it does no such thing. It's a puny exhibition, oddly squashed by where it is. Its undistinguished photographs, quaint drawings and dull, confusing models ought to sing of grandeur. Instead they merely squeak.

The exhibition's sense of bignesses belittled, of monuments made miniature, is increased by its location. To reach it one must enter the biggest room in Washington -- enter and then leave. The Pension Building's Great Hall is 16 stories high, spacious and imposing, but it still is mostly empty; the show has been installed in low galleries beyond, and the contrast is oppressive. That enormous airy room, with its columns thick as redwood trees, promises enormities. So does the exhibition. But both of them renege.

The problem is, of course, having pictures stand for buildings. Washington's museums, in fact museums anywhere, depend on the authentic. If the Air and Space Museum could not show us moon chunks, space capsules or airplanes, but only diagrams and blueprints; if the National Gallery could only display photocopies of its Rembrandts and Ce'zannes -- they'd be a lot less crowded. The TVA exhibition's photographs instruct, its wall labels inform, but most are adequately reproduced in the accompanying catalogue. The show is really not much more than a book thrown on the wall.

Old photographs depicting, say, the Washington Monument may tell us about obelisks, 19th-century Washington and the debt the city owes to classical antiquity -- but think what they leave out. Grand structures, to be understood, have to be experienced. Standing by the monument you get to feel its height, the weight of its materials and the way it rules its site. But history's grand buildings, unlike Old Master paintings, cannot be transported. And you cannot transport dams.

The new museum's scholars are not blind to bigness, or the significance of scale. Everyone who enters is given a brochure on their paramount exhibit, the grand old Pension Building itself: "EXTERIOR DIMENSIONS: 400 feet by 200 feet . . . MATERIALS: 15,500,000 bricks . . . THE GREAT HALL: 316 feet by 116 feet, 159 feet to highest point . . . " The comparable figures for the TVA's main river dams are vastly more impressive: "Kentucky Dam is 206 feet high and 8,422 feet long; it contains nearly 1.4 million cubic yards of concrete and 5.6 million cubic yards of earth- and rock-fill . . . " We learn in this exhibition that the labor force that built the Hiwassee Dam between July 15, 1936, and Feb. 8, 1940, included 1,100 men; that the 480-foot-high Fontana Dam is "the highest dam east of the Rocky Mountains"; that the man-made reservoir on top of Raccoon Mountain is drained, when power's needed, by "35-foot diameter waterway tunnels that extend 2,450 feet through the rock of the mountain to an underground generator room and thence through another 1,575 feet of tunnels to the discharge portals on Nickjack Lake"; that "1,530,000 kilowatts can be generated here, and the power plant can go from standby to full load in less than four minutes." But soon such figures blur.

Of course the projects of the TVA -- its waterways and power plants, its impressive roads and dams, and the jobs it introduced to a region long depressed -- deserve consideration.

"The greatest thing on earth is to have the love of God in your heart," said a Tennessee Valley farmer in 1940, "and the next greatest thing is to have electricity in your home."

Escaping floods is also nice; so are scenic roads, and pride, and sparkling fish-stocked lakes.

TVA began in 1933 -- Sen. George William Norris (1861-1944), the progressive Nebraska Republican, was the seer most responsible -- as a kind of social welfare project. But it did not stay one long. By the start of World War II, it had developed a supply of hydroelectric power that proved enormously useful in the manufacture of aluminum for war planes. It later would supply power to the atomic weapons facilities at Oak Ridge. "Its significance," writes Walter L. Creese, in an exceptional catalogue essay, "thus mutated from regional to international, and from a philanthropic enterprise to an eminently pragmatic one in an extremely short time."

That mutation is apparent in the shifting styles of TVA's designs. The painfully small houses that it first built for its workers were folksy and old-fashioned. Their walls were made of wood, their roofs were pitched and shingled; looking at these photographs of the town of Norris, one can almost hear the banjo twanging on the porch. Even the more modern flat-roofed, prefabricated houses built there during World War II continue to acknowledge what the architects regarded as bucolic domesticity: One interior drawing here depicts a teddy bear, for children, and -- to please their parents -- a small ceramic seal balancing a beach ball on its nose.

But TVA's huge dams, factories and power plants convey another message. Their railings and their doorpulls, and their art deco signs (often specially designed) speak, as do their concrete forms, of Brave New World technology, streamlining and power. "We wanted the dams to have the honest beauty of a fine tool," said David E. Lilienthal, a TVA director, but there is more to it than that. TVA's dismissal of classical ornament (there are no fluted columns here) and the muscular modernity of its structures sing of force and progress -- and cannot help but call to mind the autobahns of Germany, Mussolini's Terza Roma and other pride-developing projects of the time.

If one suspects a tie between these projects built in Tennessee, and those of far-off Europe, some portion of the linkage may be credited to Roland Anthony Wank (1898-1970), TVA's chief architect, an immigrant from Hungary who had been greatly influenced by the reforms of Otto Wagner and the Viennese Succession. Wank liked massive curving forms and shining bands of metal, and his sense of decoration left its mark on structures built throughout Tennessee.

His projects, while highly functional, were designed to be seen. "Beginning with Norris Dam, people were invited into the TVA buildings to enjoy them," notes Creese. "The powerhouses had reception vestibules . . . The chambers for housing the machinery came close to looking like shrines without priests, with the hum and vibration of the turbines and generators in the shadows offering the invocation . . . Harmony and order, validated and fused by the forces of concrete and electricity, were to be organized by 'efficient' managers, who appeared in unacknowledged contrast to the disorganized and inefficient hard-scrabble farmers and mountain miners beyond."

The marriage sensed in these designs -- between Viennese modernity and Tennessean rusticity -- was not always happy. "The 1930s were rich in human decency," writes Creese, "but not in soaring, masterful or well crystallized visions . . . TVA grandeur turned out somehow pinched."

So did this exhibition. Organized in 1983 by Marian Moffett and Lawrence Wodehouse of the University of Tennessee, it has since been traveling under the aegis of the National Building Museum (on F Street, between Fourth and Fifth streets NW), where it will remain on view until November.