A flea is attached to the ear of a dead mouse floating upside down in a jar of formaldehyde. The jar sits on the desk of the art director of the National Geographic, Howard Paine, 54, who is responsible for illustrating subjects that can't be photographed, such as the inside of volcanoes or the composition of a microchip. Paine is interested in everything -- the moons of Saturn, 18th-century British naval uniforms, the copulation of cockroaches -- a prerequisite, he says, for working at the Geographic.

Today it's fleas. He holds a large painting of a dozen fleas in all their hairy, articulated splendor -- dog fleas, cat fleas, bat fleas, rat fleas, even goat fleas, all different and all, yes, interesting. He carries the painting down the hall to show to an editor, encounters a Geographic writer and begins to tell him about fleas. It is a common scene at the Geographic: two adults, often bearded and in safari shirts, animatedly discussing something that would seem to be beyond the range of ordinary human concern.

The Geographic is not an easy place for an outsider to understand. Duties seem to overlap; people move from project to project across vast barriers of knowledge. Individual interest often qualifies a writer, photographer or editor for an assignment that would not come his or her way in a more rigid organization. Consider the photo staff assignment sheet for a single week, which merely includes the following:

Planets, Argentina, the space shuttle, rattlesnakes, the British Isles, Kluane National Park, New Delhi, seashells, urban raccoons, Charles Russell, the human body, the Dalmatian Coast, Vikings (not the football team), Kansas, Basque whalers of Labrador, the South Australia coast, the Maine Coast, the Earth, Sichuan province, frankincense, Spanish colonial America, Fez, peat bogs, Samoa, Moslems, early man, the Bering Sea, Annapolis, the tsetse fly, the Snake River, acid rain, Daniel Boone, the Bight of New York, pearls, gray wolves, Austria.

The connection between the editorial product and the far reaches of the Geographic's interest tends to get lost in the beige and polished cherry interior of the new building. There are genuine Indiana Joneses lurking among the partitions, their half-packed duffels hidden behind the orderly arrangements of books and photographs, but you would never suspect it if you saw them discussing fleas in a corridor. The Road to Rio Azul

Consider George Stuart, 49, the Geographic's resident archeologist, who started out as a calligrapher. "Archeology," Stuart says, "was a lateral arabesque." Now he specializes in Mayan civilization, but when he looks out of his office door in the cartography department he sees a $1.25 million Scitex computer moving mountains on the screen and accomplishing other tasks straight out of Genesis.

Stuart's expense accounts have included such unlikely items as black candles and chickens to be sacrificed in rain ceremonies. He once charged the clearing of a helicopter pad in Central America on his Visa card. Last May, the Geographic got wind of a discovery of a Mayan tomb at Rio Azul, Guatemala, and within a few days Stuart found himself in a helicopter owned by the Guatemalan air force, flying over the jungle -- and sometimes through it.

They strayed into Mexico. The pilot landed his fully armed chopper next to a man on a bicycle and, in his guns and bandoleers, got out and said, "Excuse me, but could you tell me where Guatemala is?"

He found Guatemala, then ran out of fuel. "The dashboard lit up. The pilot pounded it with his fists, shouting, 'Emergencia!' which was a big help," says Stuart. They crash-landed in a swamp, without food or water. "All I had was my Eddie Bauer bandanna and a cowboy hat. The soldiers were worried about guerrillas. They said they were going to set up a machine-gun periphery. We said, 'Whatever works.' "

Stuart drank rainwater out of orchids, a trick he picked up after 24 years with the Geographic, and the next day another helicopter arrived.

"They started throwing out chain saws, cans of peach juice and red-handled axes" for clearing a place for the chopper to land. "The audio-visual man almost got brained with an ax."

That is one story about Rio Azul you won't read about in the pages of the National Geographic. The official account was written by the editor of the magazine, Wilbur E. Garrett, who accompanied Stuart. He wrote it for the editor's page, and it is a classic of Geographic accuracy and condensation. The discovery of the 1,500-year-old Mayan tomb might not have come about if the archeologist in charge, R.E.W. Adams, had not enjoyed the support of the National Geographic Society.

There is yet another story of Rio Azul that you won't read about in the Geographic, one that says something about how the organization operates behind the scenes and something of the personality of the editor. Before the trip to Rio Azul, Garrett went to Guatemala City and met with the president, Gen. Oscar Humberto Mejia Victores. Garrett asked for assurances that the site would not be raided by looters -- who were known to have very good political connections in Guatemala -- and he asked for logistical support. He received both and shared the announcement of the eventual find with Guatemala's head of state. Finding Places to Explain

Garrett, 54, the godfather of a group at the Geographic known as "the Missouri Mafia" (graduates of the University of Missouri's journalism school), worked his way up to the editorship from the illustrations department. He has been compared by some old Geographic hands with Melville Bell Grosvenor, fast-talking and occasionally profane. Garrett broadened the mandate for more relevant journalism that began under Melville Grosvenor and continued with his son, Gilbert M. Grosvenor.

Garrett is known around the Geographic as one who expects others to perform, often on short notice and in trying circumstances. He has himself done some uncomfortable service for the Geographic in Southeast Asia and elsewhere. His editorial sessions are dominated by a jocular authoritarianism: Writers and editors tend to go on about the moons of Saturn or religious festivals on Grenada unless interrupted. Out of those sessions, according to one who attends them, come ideas for unusual contemporary stories such as ones on Burma, Kampuchea, children of the Dust Bowl, the shakeout from El Nin o, and the global opium loop.

"We try to go to places that need to be explained," Garrett says simply. "We get the stories that other people miss." Becoming a Compulsive Traveler

Geographic staffers spend a lot of time out of Washington. The strain on marriages is an accepted hazard. Wars, terrorism, political strife and general global unpleasantness have made their job more difficult and exacting, and the shifting focus of the Geographic from the academically curious to the socially engage' has contributed to the difficulties -- and to the excitement.

"We have a franchise here that's hard to get used to," says Rick Gore, 38, a Geographic writer for 10 years. "We can go anywhere to get a story. An armchair traveler fantasizes about where he would like to go. We do it."

He can't remember how many times he's been around the world. "I'm afraid I'm becoming a compulsive traveler -- it's addictive." And often less than glamorous. "When a parasite's going through your body, it's a different reality. Lying in Upper Volta, vomiting all night, I thought I was going to die and nobody would know." He had drunk spoiled camel's milk a few days before, in Mauritania.

A persistent notion is that of the Geographic writer or photographer as amorous adventurer. Most of them deny it. But one Geographic man lingered so long in a seductive tropical setting that an exasperated senior editor sent him a cable alleging that his wife was arriving shortly. The Geographic man was back in his office within a week. The 'Adventures' Editor

Much of the magazine's appeal lies in its attractive presentation of the generally inaccessible. Most readers will never go to Omachi or Bora Bora or the Ad Astra ice cap. One of the mainstays of the Geographic -- the difficult, offbeat expedition -- is the province of William Graves, listed on the masthead as the expeditions editor but known in-house as "adventures" editor. His writers are affectionately referred to as "the nut gang."

"If somebody wants to cross the Australian desert with three camels," says Graves, 57, "the memo comes to me."

A young woman did in fact cross the Australian desert with three camels, paid for by the Geographic. A teen-ager sailed around the world. Other expeditions have included nonstop flights, perilous ocean descents and Arctic crossings. The Geographic has never lost anyone on such an assignment, although some have come close to dying in the grip of polar bears and stomach ailments.

"An adventure," Graves says, "is a sign of incompetence."

Some of the expeditions don't pan out, but the Geographic is willing to invest on the chance that a record will be set or a discovery made.

"We gave some money to a guy to find a dinosaur in the Congo," says Joseph Judge, 56, the senior associate editor responsible for the writers. "That was a flier. But what if he had found a dinosaur?" Finding All the Facts

The evolution of a Geographic story is not a simple one, even for professionals who have labored before the masthead for decades. Built into the editorial process is an unusual fact-checking cadre, the researchers. They do their work after the stories have been written and try to demolish facts and assumptions of the writers so that the end product conforms to the Geographic's rubric of absolute accuracy.

"They begin with the assumption," says Judge, "that the writer is a liar and doesn't know what he's talking about."

Researchers send copies of quotations to people quoted in the stories. They seek third-party opinions and occasionally visit distant lands already visited by the writers. Those same writers expect such scrutiny and collect evidence from all over the Earth. One brought dried camel dung back to the Geographic to prove that it didn't smell. Another, writing about gold, had a frying pan made of the pure article and cooked eggs in it to prove that gold had good "conductivity." Told in the First Person

The stylistic requirements of the magazine are as rigorous. In the beginning was the word, and the word was I. "The whole Geographic rests on that upright pronoun," says Judge. "The first-person voice lends authenticity. You're in a whole different universe when you can open the hatch, step out and be there."

That first person, however, has his instructions: "Nobody's interested in the writer's aches and pains, his loneliness and sickness," Judge says. "The fact that he may be full of misery has absolutely nothing to do with what he's writing about."

A decade ago writers at the Geographic began to worry about their place in American journalism, their relevance. The so-called "New Journalism" had reached its zenith, and yet inside the Geographic they were still struggling with all those checkable facts.

"We had a hard time convincing other journalists that we had a special audience," says Priit Vesilind, 41, "and could write as well as anybody. There was some feeling of inferiority here, that people thought we were just filling in the blanks. People were always saying, 'I don't read it, I just look at the pictures.' After you've been hit over the head with that for so long, you start to feel it."

With time, the Geographic's coverage necessarily became more political and "relevant" because so much of the world was in turmoil, or in the grip of regimes whose effect on the physical environment could not be ignored. Now the writers seem uncommonly content with their lot.

There are about 20 full-time writers (the distinction between writer and editor is sometimes blurred), 26 staff and contract photographers, and a legion of free-lancers. Although black writers and photographers have often worked free-lance for the Geographic, only one black staff writer has ever been employed full time. Another is to join the staff in January.

The other side of the Geographic's editorial coin is Special Publications -- "Special Pubs," in local dialect. It enjoys less celebrity than the magazine, yet accounts for $60 to $70 million a year in revenue. It was indirectly inspired by Jacqueline Kennedy.

"The first lady wanted a photographic book done about the White House," says Robert Breeden, head of Special Pubs. She approached then-editor Melville Grosvenor, who agreed to do a book and assigned the task to Breeden, then in the photographic department. He and another photo editor, Don Crump, worked on the book at night. Its success resulted in the assignment of other "public service" books -- on the Supreme Court, the Capitol, the Washington Monument and other local worthies.

Breeden asked Grosvenor to make book publishing an independent enterprise.

Now Special Pubs puts out a product every three or four days -- films, educational kits, World and Traveler magazines and books -- some of them beyond the capabilities of other publishers. The Geographic's "Journey Into China," for instance, cost about $5 million to produce, used photographs from 10,000 rolls of film and had as many as 20 people in the field simultaneously. Pictures and Legends

Geographic photographers spend between six and nine months on their stories. They shoot 250 to 350 rolls of film, although particularly demanding subjects -- such as sharks -- can require more than 1,000 rolls.

Jodi Cobb, 38, a Geographic photographer, once found herself on hands and knees in a Jerusalem street, surrounded by tear gas and automatic weapons fire. "I thought," she says, " 'Why am I here? I'm supposed to be shooting beaches and silhouettes . . .' Between assignments is the hardest part. Your home life is a shambles. You've left a life behind that's also a shambles, the lights just went out. You try to remember who your friends are. They're all mad because you haven't written or called. The last time I came home, my house had been burglarized. I don't know if you ever come to terms with all this.

Like all of the photographers, she periodically ships her film back to 17th and M streets, where editors subject it to a device known as the "Garrett Box," named after the Geographic's editor, and the inventor. The Garrett Box enables photo editors to view blown-up slides at the touch of a button and pick "selects" -- possibly usable photographs -- out of the unending flow of celluloid.

Recently a photo editor was sitting at his Garrett Box when what is known as a "word editor" appeared in his doorway. The word editor said, "I need to blow off some steam. There was a photographer up on a glacier in Alaska after we'd already shot it. Why do we need two photographers covering the same glacier? I'm going to make some noise about this one."

When he was gone, the photo editor shrugged, and said, "He's interested in ice. There's a story about oceans that's encroaching on his turf. It happens sometimes, people get protective. The story about the planet Earth is overlapping the oceans story. The solar system story is causing some problems with the meteorite story. Then somebody else says, 'What about my asteroids?' "

"The Geographic is no ivory tower," says Carolyn Patterson, 63, the first woman editor. "You fight for everything you get, just like anywhere else. But everything is compensated by the material. Like ants. You come to work in the morning and pick up ants. You blow your mind with ants!"

She commands a phenomenon known as "legends." This does not refer to famous staffers or stories with dubious facts, but to captions written to explain the Geographic's many photographs. (The word "caption" lacks the historical pedigree of "legends.") The Geographic has 10 full-time legend writers under Patterson. "We do hard-sell copy," she says, "to lure the reader into the story."

She once hired a poet to be a legend writer, but he couldn't handle the strict word economy required. Legend writers do their own research and often travel to the same places visited by writers, collecting information. "Legends are like arias," according to one former legend writer. Explaining the Universe

"I did it," says Rick Gore, "in six months and 110 interviews."

The subject was the universe. It was first assigned to an astronomer, whose story didn't work out. The Geographic's map did work out, however, and when cartography comes up with a map, a story will be written to accompany it, even if that story encompasses all of creation.

Gore knew a lot about planets. But "that didn't mean I knew anything about the universe," he says. He set out in classic Geographic fashion -- by flying to Chile. There he talked to astronomers all day at the Cerro Tolol observatory and read about the universe while they were asleep.

He put together a list of sources and moved on.

One day in Hawaii, Gore came across a quotation written on a scrap of paper tacked to a geologist's door. He copied it into his notebook and later used it in another story. In retrospect the quote, from historian Will Durant, seemed to sum up the larger relevance of the Geographic:

"Civilization exists by geological consent, subject to change without notice."

When that change occurs, the Geographic will be there to cover it. CAPTION: Picture 1, National Geographic art director Howard E. Paine in his office. By Pat Lanza Field Copyright (c) National Geographic Society;office. (Nat. Geo. photo) ; Picture 2, Staff archeologist George Stuart. By Fred Sweets--The Washington Post3570