ON THE ZAIRE RIVER -- The most serene spot, the only serene spot, was out on the bow. The growl of diesel engines and the smell of excrement could be forgotten here. The river boat seemed to move without effort, with hardly a sound, almost outside of time. Its rusted snout hissed soothingly as it slipped downstream through the great river.

One afternoon, a father brought his son to the bow for a bath. He stripped the boy and doused him with water scooped from the river in a tin can. The small boy stood pigeon-toed, eyes closed, comfortably naked in the warm breeze. On the near river bank, birds and monkeys chattered behind a curtain of dense forest.

Young girls also came up front to tease each other's hair into the spiky braids that are the rage in Zaire. Students played checkers with beer-bottle caps. Mothers nursed babies.

The Major Mudimbi, a clumsy conglomeration of five barges tied to an aged tug boat, was sailing west along the Equator on its regular 1,000-mile journey back to the Zairian capital, Kinshasa. On Africa's most powerful river, it was returning out of the heart of the continent's largest rain forest. Each evening the boat slid into a sunset that washed the river in tangerine light.

The view from the bow, sadly, was a lie. By turning away from the sunset, by abandoning the serenity of the bow, the character of the river boat turned inside out. The Major Mudimbi became what it was: overloaded, smelly and mean.

People and livestock were everywhere. Decks were oiled with sewage. Passengers pushed for position. The boat was an accident waiting to happen -- a bleak exemplar of how poor people travel on the world's poorest continent.

At each stop, more and more passengers bribed their way aboard. The vessel had been overcrowded when it first started downriver at Kisangani. Then, there had been about 1,500 people on board. Three days later and halfway down the river, there were about 3,000.

In Zaire's rain forest there are few roads. This river is the only highway. Once every seven to 14 days, barring breakdowns, a passenger boat such as the Major Mudimbi rumbles by. If you want to travel, you have no choice but to wangle a way on board and fight for a place.

On the four third-class barges, where 90 percent of the boat's passengers were confined, nearly everyone slept on open decks or in windowless steel chambers designed for freight. When the rains came, as they did nearly every afternoon, passengers squatted miserably under woven mats or plastic sheeting.

The Major Mudimbi shifted frequently from discomfort to disaster.

Sailing upriver the previous week, a third-class barge caught fire. Several hundred passengers scrambled to adjacent barges. About two hundred people jumped overboard. Most of their goods were destroyed, and many of their animals died. Security people said only two people drowned.

On that same trip, the boat hit a sand bar and stopped dead. In third class, scores of people were jerked off their feet. There were a number of broken arms and legs.

And the food, one meal a day: rice and beans cooked with river water. The water can cause, among other things, amoebic dysentery.

"I am not going to lie to you," said Magie Lago, a 31-year-old economics student at the University of Kinshasa, a third-class passenger and a man who said he travels on the river several times a year. "The food in second and third class kills many, many people."

An on-board security official said several hundred people died on the Major Mudimbi in August from food poisoning.

As the boat grew more crowded, walking became dangerous. Passengers reported seeing three people slip and fall overboard. One was rescued by a fisherman; the others apparently drowned.

Narrow passageways on the barges were clogged with greasy tubs of palm oil, large sacks of charcoal, baskets of manioc and man-sized bunches of green bananas.

The assorted creatures, farm and forest, living and dead, smoked and dried, ripening and rotten that clogged the aisles, included chimpanzees, several breeds of monkeys, snapping turtles, tortoises, crocodiles, parrots, ducks, geese, chickens, goats, pigs, scaly anteaters, palm tree maggots, forest rats, caterpillars, snakes, dik-diks, bush bucks, large antelope and Congo clawless otters. Poached elephant meat reportedly was stored in bags in the boat's main freezer.

There were a number of polio victims traveling on the boat. In the congestion, their wheelchairs were useless. Those who moved, crawled, dragging their spindly legs over the muck-covered decks.

In the hot, thick, sluggish equatorial air, the smells generated by a river boat on this river are unforgettable. They stuck in the memory of Joseph Conrad, who traveled on the Congo, the former name of the Zaire River, nearly a century ago. In "Heart of Darkness," an autobiographical short story based on his fevered river passage, Conrad recalled rotten hippopotamus meat.

"The mystery of the wilderness {stank} in my nostrils. Phoo! I can smell it now," he wrote. "You can't breathe dead hippo waking, sleeping, and eating, and at the same time keep your precarious grip on existence."

There was no dead hippo, as far as anyone could determine, on the Major Mudimbi. But the boat's peculiarly unspeakable bouquet, as days drifted by, seemed to loosen the grip of many passengers.

THE REASON why so many people were allowed on board was money. The sergeant in charge of on-board security explained this to me and my traveling companions one evening as he mooched his regular evening meal in our cabin.

He explained that crew members, who worked for the Zairian government agency called ONATRA, which operates passenger and freight service on the country's rivers, supplemented their meager salaries by accepting bribes from people for whom there was no real room.

The scam was especially lucrative, he said, for crew members who controlled access to the first-class deck.

When the boat left Kisangani on a Monday, the 20 or so first-class compartments had been sold out. Even so, the deck was left clear. Four days later, the deck was choked with snoozing passengers, their goods and their beasts.

The sergeant (who, for the sake of his career, remains nameless) was annoyed. As a security officer, his job depended on large numbers of people not dying aboard the boat. Another fire, another sudden grounding on a sandbar could have injured or killed many people. The sergeant's authority, however, did not exceed that of the captain. And the captain, while objecting to photographs of conditions on board his boat, welcomed all new paying passengers.

Another component of the sergeant's annoyance was that the scam didn't line his pocket.

Of all the countries of sub-Saharan Africa, Zaire has the continent's ugliest reputation for official corruption and profit-gouging. The country's leader, Mobutu Sese Seko, is believed to have used his position to make himself one of the world's richest men. In so doing, according to experienced diplomats and a number of scholars who have focused on Zaire, Mobutu has legitimized and systematized graft.

"Corruption has become the system; it is a system by which the powerful exploit the less powerful, who in turn exploit the powerless," wrote Crawford Young and Thomas Turner, two of the world's leading experts on the country, in "The Rise and Decline of the Zairian State."

A journey on the river is a narrow but revealing window on this system. Those with power on the boat used it.

The captain pressed river traders to sell him fresh game at scandalously low prices. He kept it in his freezer for resale in the capital at a robust profit. Crew members supplemented their incomes by overloading the boat (and endangering the lives of everyone on it). On-board merchants sold their goods to river people (who had nowhere else to shop) at double normal retail.

The security men, as it turned out, had their own hustle.

They zeroed in on two bearded British rucksack tourists who had paid bribes to sleep on the first-class deck.

The Englishmen, who said they lived near Manchester and had been saving up for years to wander around Africa, liked to spend their evenings up on the boat's roof. There, they watched the sun go down and smoked lots of marijuana. They were not alone in smoking the stuff. Scores of Zairians did the same thing, often in front of security officials. The smell of marijuana smoke was as familiar on the boat as that of smoked fish or urine.

Security officials seized one of the Englishmen on Thursday evening, about eight hours before the boat was due to dock at the major river town of Mbandaka. He was taken to a cabin and told that he was in big trouble. Unless he paid them 10,000 Zaires ($80), he was told he would be imprisoned in Mbandaka. Negotiations ensued.

The price of the crime was reduced, after several hours of haggling, to the equivalent of $32. Security officials confiscated the marijuana, which they later smoked in their cabin.

NOT EVERYONE in Zaire, of course, is on the take. Aboard the river boat there were a number of university graduate students who said they were nauseated by corruption in their country. They talked for hours about the need for political and economic change.

One such student was a medical student at the University of Kisangani. His accommodations on the boat were 18 inches of space on a wood bench in the second-class barge. He was 31 years old, unmarried and had two years of study remaining before becoming a doctor.

The son of a subsistence farmer from Shaba region in southeast Zaire, he was paying his own way through medical school. He had been at it since 1981, leaving school frequently to find work. That was why he was headed for Kinshasa.

"When I finish school," he said, "I will go back to Shaba and be a surgeon. There are very few doctors there. Everyone who gets a medical degree either goes abroad or moves to Kinshasa to make money.

"The government in Kinshasa takes copper and cobalt from Shaba and sends back nothing, nothing."

He spoke contemptuously of the government's much-publicized commitment to economic reform, which has attracted millions of dollars from the World Bank and the International Monetary Fund. He said that, from his point of view, four years of reforms had succeeded only in lowering the standard of living among the poor. He said intellectuals at the university regarded reform under the Mobutu government as "a joke."

Scholars who have studied this country say that cynicism and despair are common among Zairians outside the golden embrace of what has been called the "kleptocratic state."

A leading Zairian intellectual, Ilunga Kabongo, has written that many of these outsiders move back and forth between moral revolt and participation in the amoral system:

They move "between religiosity and cheating, between praying and stealing -- praying at night and stealing during the day. Praying Africa awaits the miracle and urges it as a solution to illness, poverty and wretchedness. That is the Africa of the night. . . .

"The Africa of the week and the day manages to get along, the corrupters and the corrupted dying between two worlds in search of survival."

How was the student to make money in Kinshasa? How would he complete medical school and embark on a life of serving the poor in Shaba? He said he planned to smuggle soap across the Zaire River to Brazzaville, capital of the Republic of the Congo. He said there was good money in it.

With each passing day, the river grew wider and more powerful. In draining the 1.5 million square miles of the Congo Basin, it is the only river in the world to cross the Equator. It does so twice. Snaking between northern and southern hemispheres, a part of the river is always in a rainy season. Accordingly, it has a steadier and more reliable flow than the world's other great rivers.

This river is second only to the Amazon in the volume of water it dumps into the sea. By itself, the river has the capacity to generate 13 percent of the world's electricity. For all its power, on the 1,000-mile stretch between Kisangani and Kinshasa, it is glassy smooth and easily navigable.

The river and its tributaries, which form an 8,000-mile network of navigable waterways, offer the simplest solution to Zaire's most severe economic problem -- lack of transportation.

Since independence 27 years ago, more than two-thirds of Zaire's roads have fallen into disrepair and are impassable. Driving east to west across Zaire is either very difficult or impossible, depending on the season. Development specialists here say lack of transportation is strangling this vast, fertile nation.

"Zaire is stuck. The river is essential, but the government has not fully exploited that potential," says Dennis Chandler, country director here for the U.S. Agency for International Development (AID). "The Zairian government has been slow to open free markets on the river."

A European diplomat who monitors ONATRA, the government-owned corporation with a monopoly on river shipping, said the agency "has declined to the point where there is no regular barge transport." He said merchants in Kinshasa find it cheaper and more reliable to order beef flown in from Argentina than to buy beef raised on ranches a few hundred miles upriver from the capital.

A recent American survey of river and rail transportation problems found that large amounts of fuel allocated by the government for use by river boats and trains were sold on the black market, with profits going to powerful people in Kinshasa.

Of the four passenger boats that ONATRA operates on the Zaire, one is undergoing repairs, two are in service and one has been seized by Mobutu for his private use while his own river boat is being renovated.

The Major Mudimbi arrived at Mbandaka, its last major stop before Kinshasa, at 5 a.m. Friday morning. And there it sat. For passengers it was next to impossible to find out what was going on or why. Eleven hours passed in listless incomprehension. Just upriver, a score of rusted river-boat corpses were half-sunk in the shallows.

More passengers bribed their way aboard. The boat approached human-barnyard gridlock. Brown water three inches deep flowed from the toilets in second class. A number of goats had died. The sky was overcast. The river was gun-metal gray.

The torpor ended, at last, with the rumble of diesel engines and the beginning of the final leg of the journey. As night fell, the boat steered briskly out into the current.

Movement and the prospect of getting off the boat in two days juiced up the disco in the second-class barge. Cases of warm beer appeared. Amplified Zairian reggae, the best music in Africa, shook the steel floor.

Two men took center stage. One, wearing a "See Hawaii" T-shirt, lip-synched into an imaginary microphone in his fist. The second, who wore no shirt, played tin-can maracas. Prostitutes scanned the crowd, batting their lashes.

On the roof of the Major Mudimbi two giant searchlights, night eyes, cut back and forth on the river searching for the channel markers. In heavy thunderstorms, which are common on the river, the lights cannot penetrate the sheets of rain. The boat stops or risks running aground. But on Friday night the weather was good. The searchlights shone for miles.

Around midnight, the river was joined by the Ubangi, its largest tributary. The river, its volume almost doubled, widened into an inky black sea. Beams from the searchlights were swallowed in the night as they looked in vain for the far side of the river.

THE DENOUEMENT of the eight-day journey was staged on the dock in Kinshasa at 9 a.m. on a Monday. There, the beasts of the rain forest encountered the traders of the capital. The meeting turned into a riot.

The crowd at the port, a couple of thousand strong, was mostly middle-aged market women. Such women are famous in West Africa for their shrewd and aggressive trading. They had come to buy and were mashed together behind a fence. They wielded their rear-ends as offensive weapons as they fought for position near two gates.

These gates opened onto two narrow ramps that led down to the dock where the Major Mudimbi had tied up. The four-foot-wide ramps would soon become gantlets through which the market women and all the boat's passengers, beasts and freight had to pass.

When the boat first docked, a dozen gendarmes appeared to have the situation well in hand. In dark sunglasses, jet-black helmets, with billy clubs clenched in white gloves, they looked disciplined and fierce. They guarded the gates between the market women and the boat.

But when the market women caught sight of the first bundle of fresh monkeys, they pushed aside the gendarmes, squeezed through gates and thundered down the ramps.

Just then, porters were staggering up the ramps with large loads on their heads -- sacks of charcoal, steamer trunks, crates of catfish, live pigs.

Fistfights broke out. Porters were knocked off their feet. Pigs squealed and tried to bite market women. Bags of charcoal ripped open. Undeterred, the women pressed on in the direction of the monkeys. The gendarmes backed away.

In this manner, over the course of several hours, the journey out of the heart of darkness came to an end.