"How's Luis Marden?"

The refrain is the contemporary equivalent of "Dr. Livingston, I presume," resounding from the banks of greasy tropical rivers to the edge of polar pack ice. In a shrinking world, nothing has shrunk more than the domain of the National Geographic, that exotic Washington institution, nearly a century old, foster home to seekers after lost treasure and lost tribes. When Geographic staffers think they have attained some particularly remote terrain, when at last they feel comfortably lost, a native approaches and asks, "How's Luis Marden?"

A Geographic writer in the Arctic found an Eskimo living on a rocky promontory off Alaska and asked him for an interview. The Eskimo said, "I already promised Luis Marden."

A pilot in Hawaii told a Geographic photographer that he had been taught aerobatic flying by Luis Marden.

While following the ancient route of frankincense merchants through North Yemen, a Geographic writer wound up in Jordan, where King Hussein told him, "Say hello to Luis Marden."

A man who owns an island off the coast of Brazil asked a Geographic writer, "How's Luis Marden?" So did a treasure hunter in Bermuda, a dive shop operator in Tahiti, a jungle guide in Venezuela.

Luis Marden, alive and well and still writing at 71, is one of the last of the old-time adventurers, the epitome of a phenomenon once known as "the Geographic man." He traveled first class and carried an expense account book containing the entry "Gifts to Natives." The Geographic man always wore a jacket and tie to his office in the stately stone building on 16th Street NW, where the staff was small and familial and the border of the magazine was embellished with berries and laurel leaves. Retainers kept pitchers on editors' desks brimming with drinking water.

Later the Geographic man moved to a statelier stone building on 17th Street, where there was a restaurant at the top called The Masthead, reserved for those appearing on the magazine's masthead and their guests. Luis Marden was a regular there. Women were not allowed, because their presence might encourage "amorous adventures."

Some things have changed at the Geographic, in case you haven't noticed. Today a third building rises between the others like a garlanded Mayan temple, with its own stream flowing between polished granite boulders from North Dakota. There is no Masthead restaurant here, no unofficial dress code, no sexual segregation, no water pitchers. Geographic "people," as they have become, now travel business class, a fact that annoys Marden and not a few of his peers.

Founded in the old Cosmos Club in 1888 "to increase and diffuse geographic knowledge," the Geographic Society brought together scientists and learned amateurs at a time when Washington was an intellectual as well as political nexus. Professional seekers home from hot countries were as acceptable as lobbyists. Today many of them wear safari shirts in the halls of the Geographic, but Luis Marden wears pin stripes.

The institution to which he devoted his professional life is a difficult place for outsiders -- and sometimes insiders -- to understand. Areas of influence and expertise, from the microscopic to the universal, overlap in a hothouse of expendable energy and seemingly infinite means. Departments float like continental crusts on a mantle of money, and keeping track of it all has become a major enterprise.

Nurtured by Alexander Graham Bell and successive generations of his Washington family, the Geographic has become the largest scientific and educational organization in the world, with 10.6 million members and an income this year of $350 million. It has added books, films, television, educational kits and a travel magazine to its oeuvre, and consistently contributes to the store of scientific knowledge and social commentary.

Yet in some ways it hasn't changed at all. Earlier this month the Geographic announced the discovery of a Bronze Age shipwreck off the coast of Turkey, another project of scientific and historical moment, akin to Marden's discovery of the Bounty in the South Pacific three decades ago. The Geographic spends millions of dollars every year on research and exploration, and has a long, uninterrupted string of discoveries going back to the turn of the century. Some of the romance remains, although its technological component has grown exponentially, as has the cost.

The magazine itself -- without the laurel leaves -- is one of the most familiar artifacts in our cultural ziggurat, as well as a common sight in the rumpus rooms and conversation pits of contemporary America. While that other Washington bureaucracy, the federal government, labors through the political murk of successive administrations, the Geographic goes on producing its luminous compendiums of the knowable.

Luis Marden's suburban Virginia aerie was built for him and his wife by Frank Lloyd Wright, after the Mardens invited the architect to visit their land above the Potomac, touched by the roar of Little Falls.

His books line the walls, and there are reefs of them on tables and chairs, amid the acquisitions of a lifetime. Most of Marden's finds have gone to the Geographic or to museums, but a few remain: clay pipes and an oarlock recovered from the wreck of the Bounty, a battered diving helmet picked up on the Red Sea littoral, huge trout caught in Newfoundland with rods made by Marden, a Gurkha dagger from Nepal.

He wears pin-striped suits and monochromatic ties held in place by a National Geographic Society pin; his cuff links are made from nails taken from the wreck of the Bounty. His clipped white mustache recalls an era of the Autochrome camera and the long voyage. Although he retired from the Geographic after 50 years, he still has a desk there and writes occasional stories for the magazine.

Thirty years ago, researching a story about Bruges, Marden and his wife, Ethel, stayed at a Belgian inn where the proprietor discovered a wine cellar behind a false wall that had escaped German notice during two world wars. They drank their share of priceless wines -- a bit of the romanticism that touches all Mardeniana.

Nowadays wives and husbands of Geographic staff members may accompany their spouses at the Geographic's expense only after the staffer has spent 200 nights away from home.

"It's a point system," says Marden, with a touch of disdain. In the old days, Geographic people took care of themselves.

"I immersed myself in my work when Luis was gone," says Ethel Marden, a mathematician and a small, cordial woman with passions of her own. "On weekends, I flew single-engine planes out of Congressional Airport."

They met in 1934. She worked for the Bureau of Standards; he had just come to the Geographic from the Boston Herald, the son of an insurance broker. They agreed that children had no place in the life they envisioned, one full of travel and a thousand different interests.

Marden had never attended college. The Geographic hired him because he knew something about color photography, a rarity, which was done with multiple negatives, filters, plates. A few years later color would revolutionize both photography and the Geographic.

"You spent a lot of time worrying about your equipment then," he says, "about exposure and light. Now all a photographer has to do is have an idea about the kind of photograph he wants, and he can take it."

He was one of two men making up the Geographic's "foreign staff." They wrote stories and took their own photographs. Marden went first to Yucatan, and later got the bends diving in the holy Mayan well, but that's another story, as he likes to say.

"Travel in those days was long prepared and highly specialized. There were no airplanes. You took a ship and stayed longer. You had time to change gears. You had to speak the language" -- he speaks half a dozen -- "and know your way around. Now you take the Concorde and arrive before you leave. The jet plane and Coca-Cola have homogenized travel. You no longer get that marvelous white sorghum liqueur in China, for instance. You get Coke."

He spent 15 years as the Geographic's man covering South and Central America. "I hate steamy heat -- I've done my penance."

It doesn't come across in his stories. Like all Geographic writers, Marden used the famous first person, that composed, authoritative voice that fades in and out of the most unpleasant experiences. It doesn't dwell on the rotgut liquor drunk with pliant natives, or his fear of drowning while searching for a ship beneath the Pacific sands. Usually the voice is detailed, and a tad romantic.

The breeze had fallen during the night, and just before dawn the ship had almost completely lost way in the water. Her sails hung loose from the yards . . . The blocks creaked, and the chuckle of water at the bows died to a whisper. As the vessel rolled gently in the calm sea . . . her masts traced slow arcs against the blazing stars of the Southern hemisphere.

"An adventure," Marden explains, quoting the writer G.K. Chesterton, "is an inconvenience rightly viewed."

Behind him, in a plexiglass case, sits a huge, rare egg dropped by the aepyornis, 10 towering feet of feathered extinction. Marden found it on Madagascar. The story sounds more like Somerset Maugham than the Geographic: a French colonial sisal plantation, a priest in a white robe with a Gaulois dangling from his lip, a Parsee money-changer, gifts to natives, a lost beach strewn with 1,000-year-old remains of aepyornis eggs and, finally, a whole one, bought with cash and rum and some cunning.

"I had to drink a glass of that horrible rum," Marden recalls. "The tribesmen cheered, the way they do in Fiji. Remember, Ethel? There was fresh blood on the egg. They had sacrificed a chicken that morning."

"I think it was a lamb, dear."

Marden sent the Geographic a telegram: "Have found the aepyornis egg." In fact, he had two eggs. The French sisal planters -- members of the National Geographic Society, naturally -- donated the second one, which rests in Explorers Hall.

Marden had a reputation among senior editors for long silences, and longer stays. "Luis would just go to ground," says one. "We couldn't find him. Then he'd finally come home and pull out an egg or something, and redeem himself. We're going to put on his tombstone: 'This time Luis really has gone too far.' "

In Brazil, in the Bahia highlands, he discovered a small purple orchid he thought was a new species. His companion, a botanist, found two more. They named one for Melville Bell Grosvenor, then president of the Geographic, one for a Geographic editor and one for Marden. The orchids were examined by Kew Gardens, in London, and Harvard University.

"Mine was the only one that had never been described," Marden says. "It was a bit of an embarrassment." It became Epistephium mardeni.

He dived with Jacques Cousteau off the Calypso in the Red Sea and the Indian Ocean, taking some of the first underwater photographs with now antique equipment -- flash bulbs, imbued with hot wax, that cut his hands (he later wore gloves of chain mail) and crude seals to keep the water out. Exposure, shutter speed and focus had to be set before the descent; it was a victory just to get back to the surface with dry negatives.

Marden goes into another room and returns with a bit of polished metal, a drift pin made of Cornish brass, part of the Bounty. He weighs it in his hand.

"I saw the rudder from the ship in a Fiji museum in 1953, while covering Queen Elizabeth's coronation and empire tour." The rudder had been found on remote Pitcairn Island. "There was only one place to anchor. I knew the Bounty was there. I sent inquiries back to the Geographic ."

The Bounty was emblematic of splendid refuse, sunk by mutineers to avoid the entanglements of civilization a century and a half before. Marden presented the case for exploration to the editors. "Melville Grosvenor, bless his soul, said, 'Let Marden do it.' "

He received permission to search in the waters off Pitcairn Island from the governor of Fiji, a friend. For six weeks he dove in enormous Pacific swells. The locals told him he would die. Then he saw what appeared to be worms in a long sandy trench on the bottom of the island's one anchorage. They were sheathing nails, like those that now hold Marden's cuffs together, and below them lay the bones of the ship.

Marden had to get word of the archeological scoop back to the United States. Using a ham radio, he contacted a man in New England who sent this cable to the Geographic: "Have found the curlew's nest." As a code, he had mimicked an earlier cable sent by a Geographic man on the trail of the bristle-thighed curlew, so that the story of his discovery would not leak.

After Marden returned triumphantly to Washington, a Geographic editor told him, "We got some garbled cable about a bird." But they also got their scoop.

Marden had two replicas of the Bounty built in England; he and Ethel sailed them across the Atlantic. One sank on a reef in the Caribbean, but that's another story. These days Marden flies an ultralight named the Red Baron out of a Virginia meadow, for diversion.

"The classic days of the Geographic coincided with the classic days of the earth," he says. Travel, like everything else, has changed. "You used to go to Abercrombie and Fitch for outfitting. You got a good medicine kit and a pith helmet. You took quinine. Technological advance has enabled people to forget about the equipment."

He laughs, thinking about a half century at the Geographic. "I was a round peg," he says, "in a round hole."

Tomorrow: Alexander Graham Bell and the Grosvenors.