The heaviest object hanging in the National Air and Space Museum -- just under nine tons -- is an old two-engine, tail-dragging DC-3, the orginal workhorse of the airlines and the military (where they were called C47s). Over

The same behemoth, specifically its immense belly, lies on the cover of C. D. B. Bryan's equally huge and weighty "The National Air and Space Museum," a more than seven-pound compendium of photos and text that brings a new sense of awe to America's most popular museum.

Just as barnstormers, ocean-hoppers and astronauts have eternally captured the interest of Americans, so too has the Air and Space Museum, pulling in an unheard-of 20 million vistors in its first two years -- more than the Lincoln Memorial, Washington Monument, White House and Capitol combined. There is something uni-10,000 of them were built. Bearing the logo of Eastern Airlines, the museum's specimen logged more than 56,700 hours of flying time before its suspension from the rafters. [TEXT OMITTED FROM SOURCE] quely appealing about man's quest to step beyond the earth, and the museum is a lofty tribute -- not merely to the hardware of this struggle but more emphatically to the imagination of the undertaking. Somehow there's more magic in that first touch of moon rock than in 20 gazes out from the Washington Monument.

And Bryan, along with photographers Michael Freeman, Robert Golden and Dennis Rolfe has translated these wonders into a book. Admittedly, like the museum, it is a huge item -- even perhaps too cumbersome for the 8-year-old who might want to return to the SPADs or X-15 that so enthralled him on his past visit. But then, maybe 8 is a good age to realize how heavy an undertaking flight really is.

Bryan sets out its history crisply and clearly, opening with a richly evocative biography of the Wright Brothers that is followed with an equally illuminating glimpse at Lindbergh. After a brief mention of Chuck Yeager's conquest of the sound barrier, Bryan jumps to the space age with John Glenn's three-orbit journey in Friendship 7. The presentations frequently utilize two-page color photographs and extensive quotations from other sources -- one of the Wright's dairies or transcripts from the Project Mercury transmissions.

Although the book is roughly organized to correspond with the museum's compartmentalization, it does read as a sprightly history of flight. In fact, the book tends to orchestrate the museum's own design, underscoring the narrative dimension of a stroll through the building. There is a link between "The Spirit of St. Louis" and the moon rocket that goes beyond their proximity.

And, notes Byran, "though the objects exhibited in the museum can be admired for their uncanny sculptured beauty and the somethines marvelous functions they have performed, one must never lose sight of the fact that they are only the footprints left behind by humanity on its long, arduous, occasionally halting but wholly satisfactory, admirable, and inevitable journey to the stars."

And so the book leapfrogs, from French hot-air balloons to helicopters, from a simulated aircraft carrier to flight trainer, from a Piper Cub to an approach to Venus. It is all here; the sagas of the mail pilots and World War I aces; Amelia Earhart and the explosion of the Hindenberg; the dashing portrait of Harriet Quimbly, decked in satin for her 1912 conquest of the English Channel; the moonwalk life-support systems in great detail; reproductions of the museum's two 75-foot murals of air and space, done respectively by Eric Sloane, the great chronicler of Americana, and Robert McCall, who painted backgrounds for "2001"; explanations of engines and discussions of jet streams; even a replica of the "Little Boy" dropped by the B-29 Enola Gay on Hiroshima. It ends with a compact chronology of air and space milestones and a technical description of the museum's major exhibit pieces.

Despite the seeming incongruity it is appropriate that Courtland T. Dixon Barnes Byran, author of the Vietnam saga "Friendly Fire," should have written this book. His great-great uncle, Captain John Randolph Bryan, C.S.A., made three balloon ascents during the Civil War. The last turned into an inadvertent free flight when a soldier became tangled in the lines, and the balloon traveled 15 miles, landing in an orchard near the York River.

Bryan has continued the tradition admirably.