COLUMN ONE : The Road to Ruin for Rwanda : Today’s horrors are rooted in a past of ethnic hatred and the perils of an army--like many in Africa--trained not to defend the borders but to preserve the ruling hierarchy.

The explosion heard in the skies over Kigali at 9:40 on the night of April 6 caused no great alarm. The capital had been tense for weeks, and the sounds of grenades and rifle fire hardly made anyone flinch anymore.

“Nothing to worry about. Probably just thunder,” Phillippe Lambiliotte, a Belgian businessman, reassured his wife. The night was thick with humidity and heat and more silent than usual. Lambiliotte remembers hearing a dog bark. He went to sleep wondering if someone was moving around in the dark.

Someone was, and by morning the disembowelment of a luckless country had begun.

Guided by government troops, gangs of young thugs with clubs, machetes and spears rampaged through Kigali, hunting down members of the Tutsi tribe that until the 1950s had ruled the rival Hutus for centuries as feudal overlords.

At first, they chose their targets selectively, matching addresses with names on lists they carried; then, exhilarated by their thoroughness, they began killing anyone they felt like killing.

While the government-sponsored radio station RTLM exhorted, “Kill the Tutsis or they will kill you,” the organized gangs of marauders went block by block doing just that.

On one street corner, a Tutsi child lay wounded. A soldier shouted something to a woman nearby. She raised a club that bristled with protruding nails and sank it into the boy’s skull.

“I feel guilt for what I have done, but I must tell you I do not feel responsible,” the woman, Muliana Mukanyarwaya, 36, later told reporters. “I was only carrying out orders.”

It was not until noon on the first day of killing that the now-panicked populace of Rwanda learned that the nighttime thunderclap heard over Kigali was the explosion of President Juvenal Habyarimana’s plane, struck by a rocket as it approached the airport.

His death in the resulting crash, African diplomats said, put into effect a master plan that in genocidal scope and intensity would rival the horrors of Pol Pot’s Cambodia in the mid-1970s.

What has happened in Rwanda over the last two months--several hundreds of thousands killed and 2 million made homeless--may say no more about Africa as a whole than Bosnia does about Europe. Yet the tragedy could perhaps have been averted had Rwanda learned from the post-independence traumas of its neighbors: A security force whose allegiance is to a party or a tribe is a weapon that at some point will be used--at whatever cost--to subjugate the very people it is pledged to defend.

Most African armies, such as Rwanda’s, are trained not to safeguard borders from external threats but to protect a ruling hierarchy.

They are, as happened here, tools of leaders unwilling to share power as the price for peace, because to share the spoils of authority, in a society once dominated by chiefs and kings, is to suffer the ultimate indignity of no longer being boss.

So every conflict--such as that between the Hutus and Tutsis--becomes a winner-take-all confrontation.

That is a suicidal course in countries like Rwanda, where political pluralism is a murky concept and the judicial system is paralyzed, offering the guilty no fear of prosecution and the aggrieved no hope of compensation.

The result is that violence becomes an authorized function of state, often “privatized” in the hands of party militias.

The first Tutsis who migrated to central Africa with their cattle, probably from the Nile, were tall and slim, with thin lips, high foreheads and aquiline noses.

Though a minority, the Tutsis ruled the short, stocky Hutus, a farming people of Bantu ethnicity, under a medieval system known as buhake , offering protection in return for a share of Hutu crops and services. Eventually buhake became synonymous with servitude.

Belgian colonialists reinforced the caste system by favoring the Tutsis in education, commerce, government and security.

In 1959, three years before independence, the Hutus overthrew their masters, killing an estimated 100,000 Tutsis.

The slaughters continued periodically for five years and prompted English philosopher Bertrand Russell to call them “the most horrible and systematic human massacre we have had occasion to witness since the extermination of the Jews by the Nazis.”

Meanwhile, in neighboring Burundi, which had once been part of Rwanda, the Tutsi minority had come up with a solution to end ethnic competition. In 1972, it set out to kill every Hutu who had an education, a government job or money.

Within three months, the death toll reached 200,000. Hutu bodies were thrown into the uncovered cargo holds of military trucks and driven through Bujumbura in broad daylight until the capital had become as empty of Hutus as Warsaw was of Jews after World War II.

So subservient and obedient had the Hutus become to their Tutsi masters that they answered summonses to appear at local police stations, where much of the killing was taking place.

Sometimes when the death quotas had been filled, the police sent the Hutus home in the afternoon, with instructions to return the next day. Almost all did.

Today in Rwanda, it is the Tutsis who are the vulnerable ones, controlling neither the government nor the military.

By April 10, the violence had swept north, leaving flattened villages and murdered and maimed women and children in its wake before reaching this quiet little hillside town, a two-hour drive from Kigali.

The one-story stucco hospital in Gahini was built in 1927, at the end of a dirt road.

Rob Watson, a British doctor, was performing surgery in the operating room the evening the mob came up the road with its machetes. His Rwandan staff of nurses stood bravely at the door and tried to face down the wild-eyed assailants with words of reason. They were pushed aside.

As calmly as if they were on a mission to visit the ill, the young killers went from bed to bed, looking for anyone with Tutsi features.

“In the name of God . . . “ a nurse said. One of the youths ignored her and plunged his machete into the stomach of a female patient.

One group tried to barge into the operating room, but Watson put his shoulder against the door and managed to lock it. Later, the surgery successfully completed, he entered the courtyard where the killers were still milling about, and he had a chilling realization: He knew these men. They were the jobless youths he passed almost every day, the idle ones in Gahini who always looked so bored and so in need of something to do.

According to numerous Rwandans interviewed here and in Tanzania, the youths recruited by Habyarimana’s National Republican Movement for Democracy and Development to help the army and presidential guard carry out the massacres were formed into two groups: the Interahamwe (Those Who Stand Together) and the Impuza Mugambi (The Single-Minded Ones).

They were paid $3.50 a day and were drawn from the ranks of the uneducated, unemployed young men who hang out on the street corners of all African cities.

Their presence is worrisome to every African nation, and none more so than this unfortunate place best known, until April 6, as the home of the late naturalist Dian Fossey (who was murdered here) and some of the last mountain gorillas on Earth.

In a “dual society” such as Rwanda’s, with only two ethnic groups vying for power, idleness combined with overcrowding and other obstacles to development can be a prescription for hatred at close quarters, says Ali Mazrui, an African political scientist.

With nearly 8 million people, Rwanda is the world’s most densely populated nation. It had, before the recent foreign exodus, five times more missionaries (903) than physicians (177). It has the highest birthrate in the world, with each woman bearing an average of 8.6 children. Life expectancy is 47 years, and of every 1,000 Rwandans born, 189 will die before they turn 5. One-third of the adults in Kigali, the World Health Organization says, are believed to have what is referred to in Rwanda as “the famous disease”--AIDS.

Nonetheless, by the mid-1980s, Rwanda was being hailed by the World Bank as a model African country.

It had made economic reforms, and Habyarimana, who had seized power in a 1973 coup, was paying at least lip service to the need for ethnic conciliation.

John Blane, the U.S. ambassador here in 1982-85, managed to get Rwanda special U.S. economic development funds as a reward for its progress.

“I found the Rwandans to be the nicest, sweetest, most inoffensive people I’ve ever met,” Blane said by telephone from Washington. “I didn’t feel there was any nastiness in them at all. I never would have suspected something like this could happen. Oh sure, I heard some Tutsi complaints that they weren’t getting a fair share, but those complaints were never at a very high pitch.”

When Oscar and Eugenia Giordano, an American couple, arrived in Rwanda in 1991 on their first African missionary assignment, they remember seeing their new home in Mugonero, 100 miles south of Kigali, and thought that they had reached paradise. The hospital and church each stood on small hills, and in the valley between them was their house, its porch offering a superb view of Lake Kivu below.

Now, in the middle of April, three years later, Oscar Giordano was careening alone in his Trooper away from Kigali, where he had been trapped by the fighting, and back to his hospital and wife. He remembered the eerily prophetic words of a sermon he had delivered just days earlier: “If you want to give your life to Jesus, this might be your last opportunity.”

In the last 20 miles of his journey, through a valley in the shadow of death, he saw in the approaching darkness not a car, not a person, not a light.

“Never before, in three years, have I seen an African road with nobody on it,” he said. But in Mugonero a welcome sight awaited him: The hospital, the church, his home and wife and three daughters were safe.

A menacing gang of 60 or 70 men had approached the hospital the day before with machetes. They had come to the dirt road in front of the compound, then miraculously turned back.

The night of Giordano’s return, grenades were thrown into the compound, and the next morning the Giordanos packed four small suitcases and joined a convoy of Swiss and French nationals to Zaire, leaving behind the hospital where the two doctors and their staff of 75 Rwandans had cared last year for 20,000 patients, conducted 980 operations and delivered 405 babies. Their last communications with the staff was by telephone at 4 p.m. on April 13.

“They’re coming to attack us again!” shouted the voice on the other end of the line. “They’re coming again now!”

In retrospect, the Giordanos now know, it had been clear for some time that the framework was being built for Rwanda’s ultimate moment of horror.

Since October, 1990, when the Tutsi-dominated Rwandan Patriotic Front had launched a civil war, Africa Watch and other human rights organizations had documented the deaths of hundreds of innocents--mostly Tutsis and members of political parties opposed to Habyarimana--and had called for urgent reforms and a halt to the arming of civilians.

The ill-disciplined, often drunken army had gotten so out of hand that Habyarimana--who frequently had denied that his military was guilty of any excesses--called senior commanders together in Ruhengeri in March, 1993, and said, “It is always a bitter experience for me to have to castigate certain soldiers for their behavior; they are not many, but how destructive are their actions when they abuse innocent people by pillage, rape and all kinds of vandalism.”

Five months later, in Arusha, Tanzania, Habyarimana signed a peace agreement with the rebels designed to lead to a broad-based transitional government and democratic elections.

That accord may have sealed the president’s fate, and Rwanda’s. His assassination and the chaos that followed, it is widely believed, were the work of extremists in his own party who believed that Habyarimana had “gone soft on the Tutsi problem” and who were determined to derail the Arusha Accords.

The extremists are primarily Hutus from the north, the home region of Habyarimana’s Bushin clan. They are at odds with both the Tutsis and the more moderate southern Hutus who favor ethnic power-sharing.

Benedict Ndagijimana, a college freshman majoring in English, is among the hundreds of thousands of Rwandans to flee the extremists and their mindless youth militias. Many of his friends are dead. He is not sure his parents survived.

For the last two weeks of his monthlong flight to Tanzania, he hid in bushes and foraged for food. His clothes were so badly ripped by thorns and vines that he was left nearly naked. He felt, he said, that he had returned to the Africa of a century ago.

By mid-May, Ndagijimana had reached safety in Tanzania’s Benaco refugee camp--part of what the United Nations said was the “fastest, youngest” exodus of people across a border in modern times. Dressed in tattered, secondhand clothes, he had gone in a month’s time from being a member of the privileged elite to some undefined status below the bottom rung on the class scale.

How could this happen? he was asked: “It is not complicated. People who cannot read and do not have access to television believe what the government tells them on the radio. That becomes truth. They hear over and over that the Tutsis are out to kill them, and that is reality. So they act not (so much) out of hate as fear. They think they have only the choice to kill or be killed.”

And what of Rwanda?

“Rwanda is dead,” he said. “For my generation at least.”

Lamb was recently on assignment in Rwanda.