As the world notes the anniversary of the April 1994 genocide in Rwanda - a horror that ranks with Hitler's Holocaust and the Killing Fields of Cambodia as the 20th century's worst examples of mankind's capacity for evil on a mass scale - Rwanda's neighbor, Burundi, teeters on the brink of another cataclysm.

These two countries in the heart of Africa have danced a tortured tango of terror since emerging from colonial rule over three decades ago. Hutu persecution of Tutsis in Rwanda has set the stage for Tutsi persecution of Hutus in Burundi and vice versa with the seeming inevitability of a classic tragedy. Violent death has become a way of life.

The latest eruption of violence in Burundi, in late March and early April, has been relatively minor on the scale of Tutsi-Hutu carnage. Tutsi militia killed a few hundred Hutus in ``ethnically cleansing'' most of the capital, Bujumbura. A small attack on Rwandan Hutu refugees in northern Burundi led 55,000 of them to flee again, this time toward Tanzania. But Tanzania, already host to about 750,000 refugees from Rwanda and Burundi, closed its border.

Whether this will be the precursor to another round of massive killings or just another of many ugly footnotes in the lengthy history of Tutsi-Hutu horror in anybody's guess.

The situation in Rwanda, meanwhile, is also ominous. The defeated Hutu army and militia, which in April last year killed an estimated 500,000 Tutsis, await their chance to return to power.

How did these two small, remote, countries get into this situation of unremitting terror, never far from the brink of another genocidal abyss?

There are no easy answers. Perhaps there are no rational answers. But we can look to history to illuminate the tragedy. COLLAPSE OF THE OLD ORDER

Rwanda and Burundi existed as nations more or less within their current boundaries before they were made colonies, first by Germany in the 1890s and then by Belgium after World War I. Tutsis, a taller, cattle-herding, Nilotic people originally from northern Africa, co-existed peacefully with Hutus, a shorter, farming, Bantu people from central Africa.

Over time, Tutsis and Hutus developed a common language and culture, living geographically dispersed among one another in a political system somewhat akin both to European feudalism and Indian castes.

This system was undermined and eventually destroyed by colonization and modernization. When the colonial structure was removed, neither Rwanda nor Burundi was prepared for self-government.

This led to continuing instability, usually kept in check by military dictatorships, but always ready to erupt and often doing so. THE DEMONSTRATION EFFECT

The latest cycle of violence began with an invasion of Rwanda by primarily Tutsi exiles, which by 1993 had developed into full-blown civil war.

The April 1994 crash near Rwanda's capital of an airplane carrying the presidents of both Burundi and Rwanda (who were then involved in peace talks) set off the genocide there. The Tutsi-led rebels eventually ended it by defeating the Hutuarmy and militia, driving them into exile in neighboring countries.

And now, the troubles have started again in Burundi. WHAT THE FUTURE HOLDS

Will this chain of ever-worsening violence ever be broken? It is difficult to be optimistic. It will probably continue at varying levels of intensity until one group or the other - probably the minority Tutsis - is so crushed it is eliminated as a military and political threat.

There is little we or other Western countries can reasonably do to halt this process. Military intervention, which was attempted in Somalia, would probably have similar unfortunate results. And no one wants to re-impose colonial rule.

What can we do? We can continue providing humanitarian aid. We can encourage other Africans to play a more active peacekeeping role. And we can do a better job of simply paying attention. The glare of media exposure and the force of moral suasion cannot save these people from themselves; but they are the best tools available to attempt to limit the extent of this ongoing human tragedy. MEMO: J.R. Bullington is director of the Center for Global Business and

Executive Education at Old Dominion University. He was formerly a U.S.

ambassador and career diplomat.

ILLUSTRATION: REUTERS COLOR PHOTO

Hutu civilians walk across the bridge marking the border between

Burundi and Zaire on March 27. Because of a heavy military presence

in the capital, thousands fled their homes.