By NICHOLAS D. KRISTOF, The New York Times

Nov 22, 2005, Kalma Camp, Sudan — When the Arab men in military uniforms caught Noura Moussa and raped her the other day, they took the trouble to explain themselves.

"We cannot let black people live in this land," she remembers them telling her, and they used racial epithets against blacks, called her a slave, and added: "We can kill any members of African tribes."

Ms. Noura is one of thousands of women and girls to be gang-raped in Darfur, as part of what appears to be a deliberate Sudanese government policy to break the spirit of several African tribes through mass rape.

This policy is shrewd as well as brutal, for the exceptional stigma of rape here often silences victims even as it terrorizes the entire population and forces people to flee.

Ms. Noura, 22, expected to be married soon, and the neighbors said she probably would have received a bride price of 30 cows. These days, they say, she will be lucky to find any husband at all - and will not get a single cow.

This is the first genocide of the 21st century, and we are collectively letting the Sudanese government get away with it. Sudan’s leaders appear to have made a calculated decision that some African tribes in the Darfur region are more of a headache than the international protests that result when it depopulates large areas of those tribes. In effect, it is our acquiescence that allows the rapes and murders to continue.

The solution isn’t to send American troops. But a starting point is to convey American outrage - loudly and insistently - and demonstrate that Darfur is an American priority.

Ms. Noura’s saga began when the Sudanese Army and janjaweed militia burned down her village a year ago and killed her father. She and her family fled here to Kalma, but she is the eldest child and needed money to support her younger brothers and sisters.

So she ventured out of Kalma to cut grass in the nearby fields to sell. That was when the men raped and beat her, leaving her unable to walk home.

Rape leads to particular injuries in Darfur because many girls, as part of female circumcision rites, have their vaginas sewn shut with a wild thorn. The resulting physical trauma from rape also increases the risk of H.I.V. transmission. In addition, the attackers sometimes rape women with sticks or bayonets, causing internal injuries that leave the victims incontinent.

Sudan has backed off a bit in response to protests about the rapes, and it has stopped arresting women who go to foreign aid workers to seek medical treatment. But the rapes themselves are continuing, unabated. The Sudanese police and military are everywhere in the area, but they don’t secure the fields outside the camp where the attacks take place.

In just one of eight sectors in Kalma, I found three women who acknowledged on the record that they had been gang-raped this month within a few days of each other.

Arifa Muhammad, 25, told of being caught by 10 men as she planted okra to have a little more food for her three children. One of the men said, "I know you are Zaghawa, so we will rape you." Afterward, they beat her with the butts of their guns.

The very next day, Saida Abdukarim, also 25, was tending her vegetables when three men with guns seized her. She pleaded with them, pointing out that she is eight months’ pregnant.

"They said, ’You are black, and so we can rape you,’ " she recalled. Then they gang-raped her and beat her with sticks and their guns. She absorbed the beating, trying to protect her unborn baby, and although she was too battered to walk, she has so far not miscarried.

To me, Ms. Noura, Ms. Arifa and Ms. Saida are among the heroes of Darfur. There is no shame in being raped, but plenty of stigma should attach to those who ignore crimes against humanity. In my book, it’s the politicians who don’t consider genocide a priority who aren’t worth a single cow.

These three women have the backbone to stand up and be counted. We in the West have so much less to lose, yet we can’t even find our own voices. Let’s hope that the courage of these three women may inspire President Bush, Kofi Annan and other world leaders finally to show a little more backbone and stand much more firmly against genocide.