The "Magnificent Voyagers" show doesn't close here until November, and it doesn't open in Indianapolis until next February -- but people are already working full time on the move.

The exhibition, one of the largest ever mounted by the Smithsonian, has 1,750 objects, assembled by more than 20 curators from 12 departments. It sprawls over an entire gallery at the Museum of Natural History, and at that the gallery had to be completely rebuilt to accommodate, for instance, a film theater, a full-scale replica of a ship's cabin and a mural 12 feet high and 54 feet long.

The show, whose opening last summer was overshadowed by "Treasure Houses of Britain" and its royal visitors, is one of Washington's great underrated sights.

It took three years to research, two years to design and a solid year to install. Toward the end, about 80 specialists were milling around putting things in cases. Some of the items are so scarce that one Smithsonian museum wouldn't even lend them to a fellow museum right here in town. One sword alone is insured for $175,000. A Hawaiian helmet made of feathers is so fragile, old and rare that no amount of money could replace it.

"Magnificent Voyagers" tells the story of the U.S. Exploring Expedition of 1838, a sort of scientific Declaration of Independence for this young nation, covering 87,000 miles in four years. It mapped 200 Pacific islands, produced the first map of the Oregon Territory and the sw,-1 first confirmation that Antarctica was a true continent, captured 2,000 new species, adopted a cannibal king (who died the minute he saw New York) and collected the enormous mass of artifacts, maps and specimens that launched the Smithsonian Institution itself.

The material is lent by 40 museums around the world, but even so, more than 95 percent comes from the Smithsonian.

There are ship models, war clubs, baskets and pots, stuffed foxes, zoological engravings, pre-missionary -- that is to say, extremely brief -- grass skirts (there are 85 in the collection; did the thorough explorers ask everyone in the village to strip?), necklaces of teeth: shark, pig, dog, human; carved goddesses, masks, bone fishhooks, precious stones, a whole wallful of spears; exotic shells; plants (50,000 were brought back); and a stand of Norfolk Island pine trees.

"They brought all these pines back from the Pacific," says Smithsonian anthropologist Jane Walsh, who with Adrienne Kaeppler, curator of oceanic ethnology, put together the staggering anthropological collection. "When the stuff finally got to Washington the trees were gone. Maybe stolen. Years later a lot of them turned up in Salem, Massachusetts, growing happily." Some samples of the pretty, fringed trees are in the show.

And tapa cloth. Antique tapa cloth. More tapa cloth than you really wanted to see. One life-size figure of a Fiji man is dressed in a ceremonial robe made of a 400-foot strip of tapa cloth, fantastically folded and bunched like an apotheosis of the bustle. It is perhaps unique; even the Fiji Museum has nothing like it. The show also features giant squares of tapa, one of them 16 by 18 feet.

Tapa cloth, made by pulping and matting the inner bark of the mulberry tree, is extremely perishable, and when Smithsonian curators discovered these great sheets of the stuff in their storerooms, still intact, still as brightly colored as new, they considered it something of a miracle.

Incidentally, the curators wanted their life-size model for the tapa robe to have authentic Fiji features and the characteristic broad feet and hands. Searching around Washington, they found a Fiji islander working at the World Bank -- the only male islander in town aside from the ambassador himself -- and he cheerfully donated casts of his face, hands and feet to the cause. They were attached to a standard store dummy.

For some reason the remarkable adventure of 1838 never caught the world's imagination like, say, the doomed Scott expedition or Capt. Bligh's breadfruit mission in the Bounty. Yet it had all the excitement an explorer could want. One of the six ships went down with all hands. In the South Pacific, the weather was so hot the officers couldn't hold on to their sextants. And a five-minute movie made in 1929 shows what it meant to round Cape Horn in a sailing ship.

In the film, aired continuously at the exhibit, a four-masted bark shudders and bucks like a catboat under 100 mph winds, its decks buried in monstrous frothing waves, while 40 men struggle frantically shoulder to shoulder on a giant spar as they try to change a single sail, and finally the very camera is blown from its stand.

The trip, across the Pacific to Australia, to the Pole, to Fiji and Hawaii (for a sight of the volcanoes), to Oregon and back to New York, generated 19 volumes of reports and atlases. The expedition's 1841 map of Tarawa atoll is here, showing the lagoon seven to 15 feet deep. It was the map used for planning the American attack on the island in World War II. By then, however, the lagoon was much shallower, and invading forces took terrible losses as they waded 700 yards to the beaches.

There is also a map of California and the West, virtually blank from the Sierras to the Wasatch Range, with a prescient dot marking Fort Sutter, at the time an obscure trading post still waiting for Jim Marshall to spot that bright nugget in the millrace.

bat10 "Magnificent Voyagers" will travel not only to Indianapolis but also to Los Angeles, Tacoma, Wash., and Anchorage before it winds up in New York late in 1988. Moving the show is a project almost as daunting as the expedition itself.

For weeks now, the people at MFM Co., designers and exhibit specialists, have been worrying their copies of the list, reducing the 1,750 objects to 400.

This means, of course, that the whole show must be radically reorganized, its 13 sections cut to nine, the accounts of the voyage itself collected in one spot instead of meandering like a counterpoint melody through the entire exhibit.

"The focus will be sharper," says Richard Molinaroli, one of the Ms of MFM, the man who designed "Magnificent Voyagers" in the first place. "We're putting all the natural history stuff in one spot, compressing the geology section. There'll be no map section at all."

Some of those antique maps, he says, with their fine lines and fading pigments, can't take more than one foot-candle of exposure to light.

Even the things that are tough enough to survive a touring show will be treated like your grandmother's lace doilies. Conservation rules of heat, humidity, light control and mounting have to be followed. For museums that lack the expertise to build adequate cases, custom-made cases will be shipped with the show. A conservator will travel with the exhibit, which will fill two large vans.

"We already have people laboriously whittling cavities in plastic foam so that things can be fitted very precisely into them," says Molinaroli. "We have to crate the vitrine cases too: The small ones go intact, but the big ones, eight feet high, have to be disassembled."

Almost everything has to break down. The ship's cabin, modeled on a cabin in the USS Constellation in Baltimore, comes apart in 10 pieces. Built from scratch, it was a major item in the $1.2 million cost of mounting this show. The spectacular mural dramatizing the grand moment when the expedition arrived at Antarctica and determined it to be a solid land mass (some French explorers showed up at about the same time, creating a lasting controversy over who was first) was painted in acrylic and gesso on a single canvas by Washington artist Hugh McKay. It is stuck to the curved wall with a special film that will allow it to be simply peeled off and rolled up like a window blind.

Thinking ahead: The panorama of ice, sea, sky and accurately depicted ships has been designed so it can be cropped at the sides if absolutely necessary.

"The spears will travel on their own, there are so many different sizes," Molinaroli says. "Museums will have to build their own cases for those. We won't send the bigger pieces of tapa. Some of these things are so fragile it takes us two months just to make the mountings. Like feather capes: You have to build in supports for all the seams so their own gravity doesn't strain them."

Every time the show is unpacked, the condition of each item must be reported on. Rare objects are watched for the slightest sign of wear, for as Molinaroli says, "These things have already had their run of luck to survive this long."

A special setting-up kit goes with the exhibit; there is no time to let curators arrange each item to taste, so each case comes with front and side diagrams showing just where things go. And the labels. And the texts, which have to be largely rewritten.

Molinaroli picks up the thick packet of paper that contains the list of exhibits. It is covered with checks and circles and penciled remarks and a lot of initials.

"We have a long way to go," he sighs. "A lot of decisions to make. The elephant skull -- I don't know what we'll do with that.