ALONG THE CHAD-SUDAN BORDER — In June I wrote several columns about Magboula Muhammad Khattar, a young Sudanese woman whose parents and husband had been murdered in Darfur and who had escaped by night to the Chad border.

She was living under a tree there. One of her sons was then so sick, probably from contaminated water - 20,000 people were living out in the open without a single toilet - that he seemed likely to die.

On returning this month, I searched again for Ms. Khattar.

Now, each time I write about the genocide in Darfur, I hear from readers who say something like: "It's terrible to hear the stories, but face reality - Africans are always slaughtering each other." Or: "It's none of our business, and anyway we don't have extra troops to send." Or: "There's nothing we can do."

If that were true, then Ms. Khattar would now be dead.

So would the woman I'd met huddled under the very next tree, Zahra Abdel Karim, whose husband and two young sons had been slaughtered by the Janjaweed militia. She had been gang-raped along with her two sisters, who were then killed. Ms. Zahra was slashed with a sword and left to hobble away, naked and bleeding - but determined to survive so she could stagger across the desert to Chad and save her remaining child.

Yet I just had a wonderful reunion here with Ms. Khattar and Ms. Zahra, who are now fast friends. They and the other 200,000 Darfur refugees in Chad are living in camps, with tents for shelter, purified water, medical care and food distributions. Even within Darfur itself, the United Nations World Food Program managed to get food to 1.3 million people last month out of the 2 million who need it.

"It's much better here now," Ms. Khattar told me, flashing a beautiful smile as her son - now recovered - played with other children a few feet away.

I also tracked down two lovely orphans, Nijah and Nibraz Ahmed, 1 and 4 years old, whom I had met in June after their parents were both killed by the Janjaweed. Their grandmother sneaked back into Darfur two weeks ago to try to find their older brother, so their widowed aunt is caring for them. Her situation has improved enough that she fed me a home-cooked breakfast on the ground outside her tent.

The improvement for the refugees in Chad underscores how easy it is to save lives in a situation like this. Just a dollop of international attention led Sudan to rein in the Janjaweed to some degree, and to provide more humanitarian access. An international aid effort, overseen by the U.N., is saving countless lives by spending as much in a year as we spend in Iraq in a few days.

I wish President Bush had done more to help Darfur. But he has done more than just about any other leader, and his legacy will be hundreds of thousands of lives saved in Darfur - but also tens of thousands of deaths that could have been averted if he had acted earlier.

Dr. David Nabarro of the World Health Organization estimates that within Darfur itself, 70,000 people have perished since March 1 of hunger and illness. Add the deaths from violence, the deaths of refugees in Chad and the deaths before March 1, and my guess is that the Darfur genocide has claimed more than 100,000 lives so far - and the total is still rising by 5,000 to 10,000 deaths per month.

If a halfhearted effort can save hundreds of thousands of lives - without dispatching troops, without a visit to the region by Mr. Bush, without providing all the money that is needed - then imagine what we could accomplish if we took serious action.

Sudan's leaders are not Taliban-style fanatics. They are pragmatists who engaged in genocide because they thought it was the simplest way to end unrest among tribal peoples in Darfur. If we raise the costs of ethnic cleansing with a no-fly zone, an arms embargo, travel restrictions on senior officials and other targeted sanctions, then I think they can be persuaded to negotiate seriously toward peace.

The history of genocide in the last century is one in which well-meaning Americans were distressed as Turks slaughtered Armenians, Nazis rounded up Jews and Gypsies, and Serbs wiped out Bosnians - but because there were no good or easy options, they did nothing.

Note to Mr. Bush: This time, we can still redeem ourselves - but time is running out, at the rate of 200 lives a day.