THE WORLD'S response to AIDS has grown remarkably. Two major campaigns against the disease have been launched in the past three years -- the Global Fund to Fight AIDS, Tuberculosis and Malaria, and President Bush's AIDS initiative -- with the result that total spending on AIDS in low- and middle-income countries has risen to nearly $5 billion a year, up 15-fold since the mid-1990s. At the same time, AIDS activists and manufacturers of generic drugs have combined to force down the cost of antiretroviral treatment, and more leaders of developing countries have become willing to speak out about the pandemic. These developments show why defeatism in the face of AIDS is wrong. Popular outrage at the spread of a mass killer has created the will to combat it.

There is one other piece of good news, before we get to the bad stuff. Where governments have mobilized to fight the virus, they have proved that the fight can be effective. Five African countries have managed to keep infection rates below 2 percent: The fate of the rest of the continent, where infection rates above 15 percent are common, is not at all inevitable. Moreover, East Africa's urban centers have reduced infection rates -- in Kampala, Uganda, the rate stands around 8 percent, down from 29 percent a decade ago -- showing that even the worst-hit countries are capable of progress. Brazil and Thailand stand out as countries taking bold early steps that have paid off handsomely.

The bad news is that the world's expanded response still falls short of what is needed. Last year 5 million people were infected, more than in any previous year, even though improved data have led experts to revise downward the total number of people thought to be infected, from 40 million to 38 million. In southern Africa, new infections continue to keep pace with the horrifying death rate; in Eastern Europe and parts of Asia, the numbers are rising quickly. According to a new report from UNAIDS, 93 percent of patients in developing countries who urgently need treatment are still not receiving it; four out of five people in the world fall outside the reach of existing prevention campaigns. Stigma continues to frustrate the basic steps needed to confront the disease. In South Africa, for example, less than 10 percent of infected people know their HIV status.

And so, despite the recent expansion of resources to fight the disease, UNAIDS estimates that spending needs to be quadrupled over the next three years. President Bush is sticking to his pledge to ramp up U.S. spending, though this year's budget request still falls short of the annual $3 billion he promised. But the serious shortfall concerns the Global Fund. Until recently it was saying that it would need $3.6 billion next year to fund all high-quality applications, which would represent a welcome increase from the $1.5 billion in grants awarded this year. Donors have told the fund flatly that it won't get that much, so next year's target has been cut to $2.4 billion. The donors have pledged only $860 million so far.

Until now, the United States has provided more than its fair share of the fund's needs: In 2003 the United States pledged $320 million to the fund, four times as much as Japan (although its economy is just 21/2 times as big) and more than six times as much as Germany (although its economy is just five times as big), while South Korea contributed precisely nothing. But the administration's budget request this year would cut the U.S. contribution to $200 million just as the fund is trying to expand, undermining efforts to get other nations to come forward. Last week a House markup doubled that allocation, and Senate appropriators will soon have an opportunity to go even further. They must take it.