LONG THE CHAD-SUDAN BORDER — For decades, whenever the topic of genocide has come up, the refrain has been, "Never again."

Yet right now, the government of Sudan is engaging in genocide against three large African tribes in its Darfur region here. Some 1,000 people are being killed a week, tribeswomen are being systematically raped, 700,000 people have been driven from their homes, and Sudan's Army is even bombing the survivors.

And the world yawns.

So what do we tell refugees like Muhammad Yakob Hussein, who lives in the open desert here because his home was burned and his family members killed in Sudan? He now risks being shot whenever he goes to a well to fetch water. Do we advise such refugees that "never again" meant nothing more than that a Führer named Hitler will never again construct death camps in Germany?

Interviews with refugees like Mr. Hussein — as well as with aid workers and U.N. officials — leave no doubt that attacks in Darfur are not simply random atrocities. Rather, as a senior U.N. official, Mukesh Kapila, put it, "It is an organized attempt to do away with a group of people."

"All I have left is this jalabiya," or cloak, said Mr. Hussein, who claimed to be 70 but looked younger (ages here tend to be vague aspirations, and they usually emerge in multiples of 10). Mr. Hussein said he'd fled three days earlier after an attack in which his three brothers were killed and all his livestock stolen: "Everything is lost. They burned everything."

Another man, Khamis Muhammad Issa, a strapping 21-year-old, was left with something more than his clothes — a bullet in the back. He showed me the bulge of the bullet under the skin. The bullet wiggled under my touch.

"They came in the night and burned my village," he said. "I was running away and they fired. I fell, and they thought I was dead."

In my last column, I called these actions "ethnic cleansing." But let's be blunt: Sudan's behavior also easily meets the definition of genocide in Article 2 of the 1948 convention against genocide. That convention not only authorizes but also obligates the nations ratifying it — including the U.S. — to stand up to genocide.

The killings are being orchestrated by the Arab-dominated Sudanese government, partly through the Janjaweed militia, made up of Arab raiders armed by the government. The victims are non-Arabs: blacks in the Zaghawa, Massaliet and Fur tribes. "The Arabs want to get rid of anyone with black skin," Youssef Yakob Abdullah said. In the area of Darfur that he fled, "there are no blacks left," he said.

In Darfur, the fighting is not over religion, for the victims as well as the killers are Muslims. It is more ethnic and racial, reflecting some of the ancient tension between herdsmen (the Arabs in Darfur) and farmers (the black Africans, although they herd as well). The Arabs and non-Arabs compete for water and forage, made scarce by environmental degradation and the spread of the desert.

In her superb book on the history of genocide, "A Problem from Hell," Samantha Power focuses on the astonishing fact that U.S. leaders always denounce massacres in the abstract or after they are over — but, until Kosovo, never intervened in the 20th century to stop genocide and "rarely even made a point of condemning it as it occurred." The U.S. excuses now are the same ones we used when Armenians were killed in 1915 and Bosnians and Rwandans died in the 1990's: the bloodshed is in a remote area; we have other priorities; standing up for the victims may compromise other foreign policy interests.

I'm not arguing that we should invade Sudan. But one of the lessons of history is that very modest efforts can save large numbers of lives. Nothing is so effective in curbing ethnic cleansing as calling attention to it.

President Bush could mention Darfur or meet a refugee. The deputy secretary of state could visit the border areas here in Chad. We could raise the issue before the U.N. And the onus is not just on the U.S.: it's shameful that African and Muslim countries don't offer at least a whisper of protest at the slaughter of fellow Africans and Muslims.

Are the world's pledges of "never again" really going to ring hollow one more time?