A pair of legs hung out of the bottom of a Messerschmitt 262, a World War II German fighter plane. "I'm just putting the cockpit back in," said a voice from inside the plane. The voice - and the legs - belonged to Michael Lyons, a former Air Force mechanic who now restores vintage planes at the Silver Hill Museum, a sort of "attic" and workshop for the National Air and Space Museum. Special tours of this facility, a series of cavernous aluminum sheds in Suitland, are available by reservation only.

For almost a year, Lyons and his coleagues, George Genotti and Carroll Dorsey, have been painstakingly taking the plane apart and putting it back together, removing all the rust, sanding the paint off, tracing the original markings and reconnecting all the wires in the plane's engine.

"In a hundred years or so someone will come along and want to study this plane," said Lyons. "If we don't put all the parts back the way they were before, no one will know how the plane worked. We're preserving history."

Genotti, who has been an airplane mechanic since World War II, pointed to the riveting work on the side of the plane and shook his head. "It was wartime, and some of the original work was crude. Look at that - the pounded-in surfaces aren't nice and smooth. And they put tape on the joints. A good mechanic would make sure the seams matched. But they were at war and not concerned with appearances. They didn't expect the planes to last too long, anyway."

When work on all the nuts and bolts is finished, the plane will be painted with the original German markings, camouflage patern and "kill" record - it had shot down seven Allied planes. The refurnished plane will then go on exhibition either at the Air and Space Museum on the Mall or at the Silver Hill Museum.

In another part of the shed, Gary Cline and Richard Horgan were replacing rotted wood on a World War I German Albatros, the type of plane Snoopy's foe, the interpid Red Baron, used to fly.

"People always associate the Baron with the Fokker Triplane, but he really made most of his kills in an Albatros," said Cline, who used to be an airplane mechanic in the Army.

Horgan, who said he'd been hanging around airports since he was a kid, pointed admiringly at the plane's shiny Mercedes engine, which he and Cline had already refurbished. "It only has about 20 hours running time on it. Then the plane took a bullet in th fuel tank."

Using a lathe, Harvey Napier worked on a brass valve identical to the original German valve. Parts made at Silver Hill ar stamped so future generations of airplane buffs will be able to tell them from the original parts.

The Albatros and the Messerschmitt both came to the United States as war prizes and toured the country helping to sell war bonds. After World War II, the U.S. Air Force went through Europe gathering planes for a proposed aviation museum. These and other planes were stored in a closed-down warplane factory in Illinois. When the Korean War started, the factory went into production again and evicted the planes. They were sent to Silver Hill, but sat outside for several years until sheds were built and the restoration program got under way.

"This plane sat outside for so long that mice made nests in the cockpit, and their droppings caused the metal to corrode," said Karl Heinzel, who was screwing the side panels into a Lockheed XP-80, the first operational American jet fighter plane. Heinzel had just finished repainting the foot pedals.

"Then I sanded them to make them look used," he said, adding. "There's always the possibility someone may open the cockpit and look in."

At Silver Hill, airplane buffs can look into the cockpit of the XP-80.They can also count the crosses that mark where German bullets hit a SPAD XIII and see a J. V. Martin Kitten, a plane that never really went anywhere but did have the first practical retractable wheels ever made. The Sky Car, an idea that never got off the ground, is also represented. These airplanes had removable wings for when you just wanted to drive them down the highway.

The tours don't take visitors into the buildings filled with planes waiting to be spruced up and put on display. Among the planes waiting in the wings atr Silver Hill are the Stars and Stripes, which Admiral Byrd flew to the Antarctic, left in a snowbank for four years and flew back again; and the Enola Gay, the B-29 that dropped the first atomic bomb. The Enola Gay, disassembled for storage, is too large to be displayed at the Air and Space Museum or in Silver Hill's present facilities - its wingspan in 141 feet. So it will stay at Silver Hill, but is not available for viewing.