ON THE ZAIRE RIVER -- The captain, dressed in crisply pressed white pajamas, stalked back and forth on the bridge. As his boat growled downriver through a green-black rain forest, he shouted and whistled and pointed to the deck below.

There, the beasts that had arrived in the night were being auctioned. Glaring white morning light poured over heaps of mottled fur and squirming legs. It was hot and some of the carcasses were ripening.

The night's harvest was mostly monkeys -- hundreds of them, some smoked, some rotting, some freshly trapped and twitching. They were tied together by their long tails in easy-carrying bundles. There also were antelope, bush buck and a couple of giant forest hogs. A well-muscled sailor with a sharp knife and bloodstained sneakers was methodically cutting throats.

From the bridge, the captain exercised his prerogative as big man on the river. He had first dibs on the game and he bought cheap. His crew hauled the meat upstairs to his private freezer. It would be resold at a 300 percent profit when the boat docked in the capital.

In "Heart of Darkness," Joseph Conrad used this river, then called the Congo, as a metaphorical highway to the black reaches of the human soul. His short story was rooted in a journey he made on the Congo nearly 100 years ago.

"Going up that river," Conrad wrote, "was like traveling back to the earliest beginnings of the world, when vegetation rioted on the earth and the big trees were kings."

The description still holds -- "an empty stream, a great silence, an impenetrable forest." And there is still, at least to western eyes, an unnerving atavism associated with travel on the river. Where else are sailors' sneakers stained with monkey blood?

But a century of commerce on the river has tamed much of its menace and burned off the Conradian gloom. Monkey trappers carry their simian bundles around the river boat with the grim workaday manner of tax lawyers toting briefcases.

The "abominable, abominable satisfactions" that chilled Conrad have been supplanted by the more quotidian mercantile intrigues of modern Africa. Once a week for decades, the "heart of an immense darkness" has been penetrated by river boats such as this one.

Part supermarket, part disco, part abattoir, part brothel, the boat is open 24 hours a day for river business: the brisk exchange of smoked eels and frilly panties, crocodiles and condoms, giant forest hogs and Dear Heart Complete Skin Lightening Treatment.

The Major Mudimbi -- an ungainly vessel made up of five rusted barges, lashed together with cables and pushed downstream by a four-decked, diesel-powered tug boat -- is an immense, stinking, noisy, overheated, overcrowded African market.

It is choked with about 3,000 people. There are twice that many animals: a menagerie of farm, forest and river creatures, alive and dead, stuffed under benches, hanging from roofs, tied to guard rails. They all will be sold in the capital -- if they don't die, rot or fall overboard.

Each year, a quarter of a million passengers and a million tons of freight travel on the river. In Zaire, an ill-governed, impoverished country with one of Africa's worst systems of roads, river transport is a key to keeping the anemic economy alive. The future of this mineral-rich nation, nearly the size of the United States east of the Mississippi, depends on the great river.

Yet no one, except for a few journalists, masochistic tourists and other refugees from reality, travels on river boats such as the Major Mudimbi for fun. Its decks are slippery with animal and human waste. Passengers occasionally slip off the boat and drown.

The food is bad and often deadly. In August, according to an on-board security officer, the second- and third-class kitchens served up a bean supper that killed several hundred people. Third-class passengers sleep with their creatures and keep a lookout for slop tossed from an upper deck. Cholera is common.

Besides being unpleasant, it is slow. The 1,000-mile journey downriver from Kisangani to the Zairian capital, Kinshasa, takes eight days if things go well. If things don't go well, it can take two to three weeks.

Zairians who travel on the river fall into two categories:

1. Those who are poor and cannot afford any other means of transport. In an almost roadless country of 35 million people where the average income is about $170 a year, this is a very large group. Third-class barges, where a ticket costs $17, are always sold out.

2. Those who want to buy goods and/or make money. At the top of this group is the captain, the man with the white pajamas, the private freezer and the power to dictate his own prices. At the bottom are river people who briefly board the Major Mudimbi to trade, hopefully not with the captain. In between are the petty commercants who reserve second-class compartments and sell their wares to river people at inflated prices.

Besides essentials such as soap and fishing hooks, the river boat sells good times. For fishermen and hunters of the interior, the boat is a movable feast: warm beer, loud music and fancy city women. Bright lights on a dark, dark river.

LURCHING ALONG the Equator through a forest that for Conrad contained the "stillness of an implacable force brooding over an inscrutable intention," the river boat is a money-grubbing interloper from the late 20th century, a garrulous whore passing through a gloomy church. It is a paradigm of how modern Africa degrades, delights and rips off rural people.

The end of the line for river boats traveling east from the capital is Kisangani. Just beyond the town is a series of impassable rapids. When Conrad signed on as a river boat captain on the Congo in 1890, his journey ended at Kisangani. It was the Inner Station, the heart of darkness.

It was carved out of the bush at the end of a network of river trading stations. The network was run by Belgian agents who were in the employ of a colonial creation unlike any other in Africa. The Congo Free State belonged to one man, King Leopold of Belgium. His agents presided over the collection and export of ivory and rubber, and Leopold pocketed the profits.

It was a savage operation. Quota systems were established for production of rubber and ivory. Those who failed to meet the quotas were beaten, raped or killed by soldiers of the Free State. To prove they had been enforcing the quota, soldiers cut off the hands of those they punished. Smoked hands became a kind of currency. Conrad called it "the vilest scramble for loot that ever disfigured the history of human conscience."

Under pressure from world opinion, the Belgian government took Leopold's grotesque kingdom away from him in 1908. The Congo slid into a half-century of paternalistic Belgian rule. Then, along with the rest of colonial Africa, the Congolese people demanded independence. The new republic -- a seemingly ungovernable amalgam of 200 tribes, no single one of which was more than 4 percent of the total -- stumbled through five years of anarchy. In the mid-1960s, one man again seized control.

In the Congo Free State, as Conrad wrote, it was impossible to travel the river without feeling the rapacity of Leopold. In modern Zaire, as passage on the Major Mudimbi demonstrates, it is impossible to travel the river without being enveloped in the power of the man who reinvented the country and created the mentality by which it still is run.

He renamed the country. He renamed the capital. He renamed the river. He renamed himself.

Christened Joseph Desire Mobutu, he became Mobutu Sese Seko Kuku wa za Banga, which translates as "the all-conquering warrior, who goes from triumph to triumph."

His photograph, with a leopard-skin cap on his head, presides over every office and many homes in Zaire, including the first-class dining room of the Major Mudimbi. Tens of thousands of Zairians, including hundreds of passengers on the boat, wear clothing made of material that bears his image. Government-controlled media call him the Guide, the Chief, the Helmsman, even the Messiah.

Mobutu, 57, the son of a cook and a hotel maid, is what African scholars call a patrimonial leader, which means the unity of Zaire is embodied in him. Those who know him say "charm drips off the man." In the capital, diplomats become weak-kneed talking about his "formidable charisma." Without Mobutu, they say, Zaire could easily devolve into tribal chaos.

AFRICAN SCHOLARS also have come up with a name for the type of governmental system that Mobutu, after 22 years in power, has devised: a kleptocracy. From the top down, the system is greased with graft.

In testimony before Congress six years ago, his former prime minister said that between 1977 and 1981 Mobutu illegally transferred more than $200 million of government funds to his personal account abroad. He, his wife and his immediate family have vast holdings in the country's mining, diamond and agricultural industries. He owns estates in Belgium, Switzerland, France and the Ivory Coast. Estimates of Mobutu's personal fortune are as high as $5 billion.

"There was and is yet a single major obstacle which annihilates all perspective of {economic} improvement {in Zaire}: the corruption of the ruling group."

So wrote Erwin Blumenthal, a West German banker, who came to Zaire in 1978. As a representative of the International Monetary Fund, he came to try to clean up the country's finances. He left a year later in disgust.

Since Blumenthal wrote his report, the World Bank has committed $602 million to Zaire. The IMF has lent even more. In return, Zaire's government has devalued its money, cut its deficits and streamlined its administration. But current representatives of multilateral lending organizations say it is "naive" to believe that much of this money is not siphoned off at the top. Said one: "The little guy on the street gets none of this."

The ethic of corruption persists in Zaire, according to bankers, diplomats, students and businessmen. It is a trickle-down system. Ministers demand payoffs for construction projects, teachers demand payoffs from their students, policemen stop motorists to give them a choice between a payoff and arrest.

"It's like termites nibbling away at the structure of a society," said one long-term observer.

The termites began nibbling before the Major Mudimbi left the quay at Kisangani. The official who checked my international certificate of vaccination noted that the cholera shot, good for six months, had expired. He was sorry, but travel would be impossible.

But wait, he said, opening a drawer and pulling out an Officier de Quarantaine rubber stamp. For 300 zaires ($2.40) and without using a needle, he made me legally immune from cholera.

A rather larger nibble in river service was taken this year by Mobutu himself. The Guide likes to entertain foreign dignitaries and visiting businessmen by taking them on river cruises. With his private river boat in dry dock undergoing renovation, Mobutu this spring confiscated one of the three functioning river boats that haul passengers from Kisangani to Kinshasa. The boats are the property of a state bureaucracy called ONATRA. Since the spring, the Major Mudimbi has been more overcrowded than usual.

The boat inched away from the dock at 1 p.m. on a Monday, nine hours behind schedule. Several hundred people had come down to the quay to see it off. As they waved goodbye, a mobile crane hoisted stacks of loose lumber over their heads. The mood was festive. No one was hit by falling wood.

On board, the captain, not yet wearing the pajamas that were to be his command outfit, strode the first-class deck, shaking hands with passengers. They included a portly major in the gendarmerie, who was traveling downriver to take up a post in the town of Mbandaka. He was traveling with his two wives, 12 children and a dog. He wore a Mobutu shirt and sat amiably in a wicker chair in front of his compartment. The major was one of about 10 police and security men on board. They made their presence known as the days passed.

Other first-class passengers included students going to the university in the capital, Asian and Zairian businessmen and some scruffy British and American tourists. Ten of the Americans were on a four-month trek called Encounter Overland and were bound for London by way of central Africa and the Sahara. They normally traveled in the back of a truck and cooked their own food. On the boat, they had third-class tickets but had paid bribes to sleep on the roofs of first-class cabins. They traveled hard and dirty and looked it.

Like many of the trekkers, Julie Gunn of Brighton, Mass., was an escapee from her profession. She said she was an intensive-care nurse in Boston, where she had seen too many affluent teen-agers overdose on cocaine and recover with the help of $20,000 of their parents' insurance money. She also said she worked in fear of AIDS-tainted blood. Traveling in Africa, the 32-year-old nurse said, was a way to forget the hospital: "It is like living National Geographic."

On the second-class barge, passengers had come not to forget their professions, but to pursue them. River merchants had booked all the second-class compartments. As soon as the boat got under way, they unpacked their wares and set up displays in the narrow passageways -- clothing, soap, nails, fishing line, cosmetics, plastic buckets and lots of drugs (penicillin, tetracycline, antimalarials, antidiarrheals, all-purpose tonics). Nearly everyone sold hypodermic needles. Many drugs were "for intramuscular injections only." The merchants said river people believe in the curative power of needles.

When they had finished unpacking, the merchants sat on benches and waited for the river to serve up some business. One shirt salesman sat quietly, squinting out at the river, which was silvery white in the midafternoon sun. He shared a cigarette with a chimpanzee that sat beside him in a cage. A goat, tied up under his seat, timidly chewed on the cuff of his trousers.

Soon after the colonial ruins of river-front Kisangani had slipped out of sight, the forest asserted itself -- 60-foot-high walls of vegetation sprang up from both sides of the river. From beneath the bush, scores of dugout canoes materialized, racing to intercept the river boat. Customers!

The docking of the dugouts, accomplished while the boat sailed at full steam (about 10 miles an hour), proved the major entertainment of the journey. It is an athletic event somewhat akin to rodeo steer wrestling.

The dugouts, fashioned by hand from giant trees, were about 40 feet long, three feet wide and wobbly. They were paddled into position downstream from the river boat. When the angle was right, the canoeists (usually two lean young men) paddled frantically to intercept the boat. The man in the bow then had about two seconds in which to throw down his paddle, spring onto the river boat, brace himself and reach back for a rope to secure the dugout.

It was a high-stakes game. Once every 20 or so dockings, something went wrong. A month's work -- embodied in crates of smoked monkeys, bundles of hand-woven mats, buckets of edible maggots -- tipped over in the river. The canoeists swam home.

If they made it aboard, the river people were suddenly hostages to the professional buyers and sellers who had been waiting for them. As a rule of thumb, merchants said, they buy game, fish and agricultural produce for as little as one-fifth the price they expect to sell it for in Kinshasa. They gave a trapper $2.10 for a fresh monkey and planned to sell it for as much as $11. Merchants said the standard mark-up on goods they sell to the dugout people was 200 percent higher than retail in the capital.

Monkey trappers, especially, argued about the low prices, sometimes screaming in rage and refusing to sell. But they had no choice. The river boat is the only store in the forest and merchants on board collude over prices. Gouging by middlemen is a time-honored tradition in Mobutu's Zaire. The longer the trappers dickered, the farther they had to paddle upstream to get back home.

Late Monday afternoon, one of six live crocodiles that had been tied up down in the engine room was brought up for slaughter. Seven feet long and trussed to a thick wooden pole, it had been loaded on board at Kisangani. It was bound for the captain's freezer.

On the open deck where the sailor with the sharp knife cut throats, the crocodile was gutted. The spectacle attracted the cameras of rucksack tourists and of the photographer who was traveling with me. The captain, stalking the bridge above, did not like it. Film would be confiscated, he bellowed in French, if anyone took pictures of a situation bizarre. The evisceration of any beast headed for the captain's freezer, it seemed, was a situation bizarre.

That evening, a sergeant in charge of security on board the Major Mudimbi paid a visit to the cabin I shared with the photographer and another journalist. He said the captain's prohibition on photographs would be no problem. He would handle the captain. He would protect us. He would be our friend.

All we had to do was feed him and buy him beer for the next seven days.

NEXT: Steaming to Kinshasa