KAMPALA, Uganda—Ninsiima Agatha, a 20-year-old mother of two, showed up at a medical clinic here last month, weak, coughing, and desperate to save herself and her two children. She had just discovered that her husband was infected with HIV—and now she had the virus too. If she didn't get access to life-saving drugs quickly, she could easily pass the disease to the baby she was breast-feeding.

But the staff at the Joint Clinical Research Centre had to tell her the bad news. Even though her husband, a clothes merchant with a girlfriend on the side, was already receiving the so-called AIDS cocktail of drugs elsewhere, there would be none for her. The clinic had enrolled its full quota of patients under its contract with the U.S. government. Ms. Agatha, sprawled on a hospital bed with a toddler and an infant, could barely move. "I feel desperate," she said.

Seven years after the U.S. launched its widely hailed program to fight AIDS in the developing world, the battle is reaching a critical turning point. The growth in U.S. funding, which underwrites nearly half the world's AIDS relief, has slowed dramatically. At the same time, the number of people requiring treatment has skyrocketed.

And lately, the global campaign to prevent new infections has suffered some reversals. In Uganda, a lush East-African country that once stood out as a shining star in the fight against AIDS, the rate of HIV in the population has begun to tick up again after a long decline. That's putting an even greater strain on a health system that's struggling to cope with the hundreds of thousands who already have the disease and could be a harbinger of what's to come in the rest of Africa.

"I personally worry that Uganda showed the way on how best to fight the disease and now is in danger of showing how to lose the fight," says Dr. David Serwadda, a professor at Makerere University School of Public Health in Kampala and a pioneer in researching the origins of the AIDS epidemic.

The most immediate concern is getting enough lifesaving drugs to all those who need them. Under the Bush administration, the President's Emergency Plan for AIDS Relief, or Pepfar, set aggressive goals for getting people with HIV, the virus that causes AIDS, into drug therapy, eventually enrolling some 2.4 million by the end of last year.

Eric Goosby, President Obama's AIDS czar, said the president is committed to the AIDS fight despite the global economic decline, adding that the U.S. doesn't intend to turn away anybody who needs treatment: "Our commitment to universal coverage hasn't wavered."

The challenge is enormous. Some 33. 4 million people worldwide have HIV, and under new guidelines by the World Health Organization, the number eligible for treatment has grown to 14 million, dwarfing the 4 million in treatment currently. Another 2.7 million people become infected each year. Those who don't die first will eventually need to take antiretroviral drugs, a mixture of medications that helps the body suppress the disease and must be taken every day for life. The therapy, which doesn't cure AIDS but allows people with HIV to live normal lives, means the number of people who need drugs will continue to grow.

One irony is that lifesaving medicine makes the prevention message harder to deliver. That much is clear in Uganda, once a leader in preventing the spread of HIV.

In the 1980s, long before foreign aid groups arrived on the scene, President Yoweri Museveni grasped the seriousness of the disease, known as "slim" for its debilitating effects. He made it his personal mission to mobilize the country. At the time, there was no known treatment for AIDS, which at its peak infected around one in five Ugandan adults.

The government's message was simple, delivered relentlessly on radio to the sound of beating drums: AIDS kills. In 1988, Ugandan music sensation Philly Lutaaya announced he had AIDS and spent his final days, gaunt and ridden with sores, touring the country to raise awareness.

The solution was a homegrown remedy that came to be known by its shorthand, ABC. The only escape, went the government message, was to practice abstinence until marriage and to be faithful afterwards—and if all else failed, to use condoms. The prevalence of AIDS eventually fell to around 6% of the adult population, and ABC was soon in use in much of Africa.

But over time, Ugandans agree, they let down their guard. Some here say it was only natural for President Museveni to declare mission accomplished and move on to other pressing needs. Others say ideological battles in Washington played a role. U.S. congressmen quarreled over how much of the growing AIDS budget should be allocated to preaching abstinence and fidelity and how much to condom use. Nongovernmental organizations here that were accustomed to advocating a range of prevention options say they sometimes felt paralyzed.

But the biggest distraction from prevention was likely the sudden flood of lifesaving drugs beginning in 2005. Fear of HIV dissipated as memories faded about the disease's ravages. People gradually increased their number of sexual partners again. "Women are now more scared of getting pregnant than getting AIDS," says researcher Phoebe Kajubi, who conducted a survey in a poor area of Kampala funded by the AIDS Prevention Research Project at Harvard University.

"People think that when they get [anti-retrovirals] they get cured of HIV," says Joseph Lubega, a 30-year-old electrical engineer-turned AIDS activist. His cubbyhole office is crammed with tens of thousands of free condoms that go unclaimed. "People aren't using condoms like they used to."

The result: New infections have begun to jump again, to around 135,000 per year, and prevalence is believed to be approaching 7%.

The increased infection rate is putting a heavy burden on health-care providers such as JCRC, one of the preeminent research and care facilities in the country. As one of the early recipients of Pepfar money, JCRC aggressively enrolled people, swelling to 32,000, and hitting the limits of its contract even during the Bush administration. The campus has tents set up to handle the overflow of patients, and now sees over 300 people every day. It routinely turns away new enrollees now.

"The dilemma here is that we made a promise to patients—if they came here for HIV care, we said if you qualify for treatment, you'll get treatment," says Dr. Fiona Kalinda, clinical manager. "Now we have to tell them to go elsewhere."

In the case of Ninsiima Agatha, turned away last month by JCRC, no other clinic would take her on. And the news soon got worse.

Dr. Peter Mugyenyi, JCRC's founder, says he just learned that Ms. Agatha's older child, an 18-month-old girl named Natero Mariam, died on Jan. 7 of AIDS, despite receiving drug treatment funded by the Clinton Foundation. Defying instructions from the U.S. not to add new enrollees, Dr. Mugyenyi says he's decided to begin dispensing drugs to the mother so that her remaining child, two-month-old Anisha Nabuuma, doesn't also catch HIV through breast milk.

"The cheapest way to save the child is to treat the mother. In the process the mother's life will be saved too," he says. "Without doing this my conscience would be haunted."

Meanwhile, he's still trying "desperately" to find spots at other facilities for 82 women he can't accept into treatment. What's more, clinic doctors have detected disturbing cases of patients who are already on medication who are sharing their supplies with partners who can't enroll, In those cases, each patient gets too little medicine, raising fears that the practice could spawn HIV strains that are resistant to ARVs. "What's going on is terrible," he says.

At Catholic Relief Services, another big treatment provider, officials say they stopped taking all but a few new patients a year ago in Uganda. Jack Norman, country representative, says blocking new patients from drugs encourages the disease to spread. For one thing, people on ARVS are less contagious. "No drugs means no hope; people don't get tested and they run around and infect other people," he says. "It's a very dangerous cycle."

In theory, the Ugandan government will eventually take greater control over treatment, as more doctors and nurses get trained under U.S.-led programs. But that day is clearly far off. Last year, the U.S. provided $285 million toward Uganda's HIV/AIDS prevention and treatment efforts, or about 70% of the country's budget.

In many parts of the country, poverty is the biggest enemy. In the dirt-poor northeast, Amuria district health officer Dr. Eumu Silver makes the two-hour trek himself to tend to the people in one village because he can't find anybody else to take the job. The region has been beset by war, cattle rustlers and now an entrenched drought. Herded into refugee camps, people spread the AIDS virus like wildfire. About 350 are currently on treatment, but Dr. Eumu figures as many as 600 are sick enough to qualify—if the single testing machine in the nearest big town weren't constantly on the fritz.

At a recent gathering in a village, people with HIV made known their needs. For one man, it was simple: He wanted a bit of porridge to take with his medicine, because it's hard to absorb on an empty stomach.

Back in Kampala, another drama was unfolding. Eve Nakitto, a 23-year-old woman with a 5-year-old daughter, had been diagnosed with HIV a month earlier and had sought treatment at Family Hope Centres, a facility run by the U.S.-based Children's AIDS Fund. The clinic didn't have any slots available and sent her to find treatment at one of a number of government facilities that theoretically had openings. But after seeking help for a month—including lining up for four straight days at one facility to no avail—she was back.

After a pleading phone call, the clinic medical director managed to scrounge a slot. Ms. Nakitto's eyes welled up, and she spoke of people in her neighborhood who didn't even bother to get tested now. "They don't want to know their status," she said. "Some don't want to be depressed."