Shrouded in inch-thick dust in a tomb-cold hangar in Silver Hill, Md., the swastikas, red circles and bullet holes are dimly visible on the killing machines men flew in World War II.

The dismantled German, Japanese and American aircraft, some rusted skeletons and others mummy-wrapped in plastic, lie in rows like caskets, hidden from the public until the day Congress allows the Smithsonian Institution to resurrect and display them.

The fighters are among the many aviation artifacts that sit in storage because the National Air and Space Museum on the Mall has no room, and because efforts to build an annex have remained grounded in congressional committee rooms.

"Even if we started to restore them, where would we put them?" said Alice Mennell, a local aviation buff, as she guided visitors through the crowded hangar at the Smithsonian's Paul E. Garber facility, where the Air and Space Museum stores and refurbishes some of the 330 items in its collection.

The 10 million visitors a year who tour the main museum on the Mall see only about 75 pieces of the collection, which traces aviation history from the first wooden framed planes with canvas wings to the more recent satellites, missiles and moon landers.

Aviation fans who find their way to the Garber facility at 3904 Old Silver Hill Rd. can see 192 air and space craft in the hangars. Another 45 pieces are on display throughout the country and around the world.

The Mall museum lacks the space to show off some of the largest jewels in the Smithsonian's collection, such as the space shuttle Enterprise, which sits outside on the pavement at Dulles International Airport, and the Enola Gay, the B29 that dropped the atomic bomb on Hiroshima, which is being restored at Silver Hill.

The dream of the museum's directors and aviation fans is to build a museum annex, a number of vast hangars to shelter and exhibit artifacts at Dulles or Baltimore-Washington International Airport.

Museum planners envision building four hangars, which would include space for the big aircraft, an area for visitors to watch restoration work in progress, a theater, a cockpit to climb into, and a simulated airport control tower where visitors could listen to conversations between nearby pilots and air traffic controllers.

"It's important that people be able to see these artifacts . . . if we want to maintain leadership in technology, if we want to inspire our nation's youth to greater achievement," said Thomas G. Morr, president of the Washington Airports Task Force, a private group that promotes Dulles and National airports.

The four hangars would create more exhibition space than exists at the main museum. The museum's two floors have about 200,000 square feet of exhibition space, said Donald S. Lopez, deputy director of the Air and Space Museum. The four 70-foot-high hangars would cover 300,000 square feet of ground on just the first floor.

Planners estimate the construction costs at $100 million over 10 years, as the annex is built in phases.

Supporters believe all the construction money can be raised privately, but they say that they cannot start raising funds until Congress approves the annex, which would be operated by the Smithsonian with federal money.

"The money is out there," said Leo Schefer, a vice president of British Aerospace Inc. and president of the Air and Space Heritage Council, a nonprofit group formed to support the annex efforts. "There's a lot of interest in space."

The council, which has supplied about $400,000 worth of services for site evaluation and other early design work, estimates that the first phase of the annex could be built within two years after Congress approves the project, Schefer said.

Legislation to authorize the annex has been passed twice by the Senate but has been grounded in the House. Supporters are readying to renew their lobbying efforts in the House during the next year.

"There's a great deal of interest {in the annex} and a great need for it," said Rep. Benjamin L. Cardin (D-Md.), who has introduced legislation to authorize the project. "It would be an instant success."

If the House does pass the legislation, it may be dragged into a competition between Dulles and BWI over where to build the annex.

The Smithsonian regents have voted to put it at Dulles, and the Senate bill and one House bill name Dulles as the location. However, the prospect of an estimated 6 million tourists visiting the annex each year prompted the Maryland state government to recommend BWI.

BWI officials have started studying the feasibilty of constructing the annex at the airport, while state officials argue that BWI would be a more convenient location because it sits just off the Baltimore-Washington Parkway, between the two cities, and has its own Amtrak station.

The annex "would be an economic boon for the state of Maryland," said Monica Healy, director of Gov. William Donald Schaefer's Washington office. Cardin's bill would allow the museum annex to be built at either of the two airports. "Congress should not select the location . . . but I also think BWI is an ideal location," he said.

Morr of the airports task force said it would cost $1 million to move the space shuttle from Dulles to BWI because the vessel must be carried piggyback on a Boeing 747. Dulles is storing several other aircraft that would be shown at the annex, including a B17G Flying Fortress and a Vought RF8G Crusader.

"I think that decision {to build the annex at Dulles} is pretty much made," Morr said.

The Enola Gay is among the planes that would be displayed at the annex. Today, the nose of the aircraft that carried the bomb sits in a Garber facility workshop, surrounded by ladders and tools; the tail section of the fuselage sits at one end of another hangar, while its wings and engines lie stacked against a wall at the other end.

"Whether you are appalled by nuclear weapons or think we have to have them, that airplane makes you think," Schefer said.

Another aircraft that might be displayed at the annex is the "Caroline," the Convair 240 that John F. Kennedy flew in during his presidential campaign. The plane's interior is on exhibit at the museum on the Mall, but the shell stands outside a hangar at the Garber facility.

Another likely annex candidate is the last Arado 234B, the world's first jet-powered bomber, built in Germany and flown in 1944. "It's just too big to keep it here," said Mennell, the Garber volunteer.

"Most everything you see here is one of a kind," said Richard Horigan, who oversees aircraft restoration at the Garber facility. To him, the pieces in the Air and Space Museum's collection "deserve the same consideration as the arts; they just take up more space."