As a longtime health volunteer in the narrow alleys of her hillside neighborhood, Ebon Sunarti has focused on corralling other women into the local clinic so their toddlers could be vaccinated against a range of childhood diseases.

But when polio broke out in her province this year and the government launched a regional campaign to immunize all children under 5, this tough-minded mother held her own 3-year-old daughter back after seeing spurious television reports that the vaccine had made many youngsters sick, even killing a few.

"This is my mother's heart. I have to be so careful," explained Sunarti, 35, her brown eyes warm but adamant.

With polio now spreading faster in Indonesia than anywhere else, U.N. health experts and local officials are struggling to counter rumors that the vaccine is harmful, and to contain the outbreak before the coming rainy season turns it into a full-blown epidemic.

The next test comes Tuesday when Indonesia plans to immunize 24 million children under 5. If the nationwide drive succeeds, it could turn back polio at its farthest frontier since the disease erupted in Nigeria two years ago. But if it fails, international health experts warn, the outbreak could spill over Indonesia's borders to other East Asian countries, dealing a setback to global efforts to eradicate the illness.

"What we have now is a looming crisis," said David Hipgrave, UNICEF's chief for health and nutrition in Indonesia.

The country had been polio-free for a decade until a traveler from the Middle East brought it to Indonesia's main island of Java early this year. The disease has now spread from the Java mountains to the nearby island of Sumatra and north to the capital, Jakarta, infecting at least 226 people.

In May, Indonesia launched a drive to vaccinate children in Jakarta and two neighboring provinces, dispatching health workers into jungles, slums and remote ridgeline villages. The effort exceeded expectations, with more than 6.5 million immunized.

But accounts of four children who died shortly afterward were reported at length in the national media. Though the World Health Organization determined that the deaths were unrelated to the vaccine, Indonesian health officials initially did little to debunk the rumors. So in a second round of vaccinations in June, intended to give the same children another crucial dose, many parents turned the health workers away, and about 725,000 fewer children got the vaccine.

"There were so many cases in the media from every place about children getting fever or getting diarrhea after the first vaccine," Sunarti said. "Many people were afraid the same thing would happen to their child."

In May, Sunarti had taken her daughter, Balqis, to the local clinic to be immunized. But she balked in June because the girl had a cough. Recounting this, Sunarti repeated the common refrain that the polio vaccine can be deadly for children if they are at all unwell.

Her neighbor, Cholifah, also turned away the health volunteers, claiming her son had mild diarrhea. "I learned from the television reports that it is best not to give a vaccine to a baby who is not fit," said Cholifah, 27, furrowing her brow and cradling the boy close.

Hipgrave stressed that the vaccine was safe, even for children who are sick. The four youngsters who died were among the 2,000 children who die every day in Indonesia from dengue, malaria and other ailments, he added.

But now, on the eve of the country's first nationwide vaccination drive, U.N. officials acknowledge that their message has been drowned out by the negative reports on television and in newspapers.

The dramatic decline in vaccinations two months ago, coupled with the spreading outbreak, sounded alarms at the far-off headquarters of U.N. agencies. Last week, WHO sent David L. Heymann, the chief of its global polio eradication program, to Jakarta to secure senior government officials' support for next week's vaccination drive.

Heymann said he was particularly troubled by the spread of the disease to Sumatra, which was battered by the Dec. 26 tsunami. If the virus reaches the western end of the island, where the health care system was destroyed, containment could prove almost impossible, he said. The eradication effort would also become more daunting if polio spread to densely populated Jakarta.

Heymann added that the arrival of the rainy season next month could accelerate the transmission of the disease, which is spread through contaminated water, as streets flood and children play in the mud.

Winning public support now is crucial, he said: "What we don't want to see is rumors get out of control and stop progress like in Nigeria."

The strain of polio now circulating in Indonesia originated in northern Nigeria, where the overwhelmingly Muslim population turned against vaccinators after rumors spread that immunization was a Western plot to weaken Islam by causing sterility or AIDS.

But in Indonesia, the resistance has no religious overtones. In fact, the country's most popular Muslim televangelist, Abdullah Gymnastiar, has been enlisted to publicize next week's drive. The Indonesian Council of Ulemas, or Muslim scholars, has issued a fatwa, or edict, endorsing the vaccine.

Some of the deepest skepticism is in Depok, the sprawling town south of Jakarta where more than a fifth of the children vaccinated in May were kept home a month later. Last week, medical officers called together three dozen volunteers, all middle-age women wearing conservative Muslim head scarves, to rally them for the drive.

"Why did so many parents keep their children home last time?" asked Deksiana Farida, the stout, dark-haired woman in charge of immunization at the local clinic.

"Takut!" the women answered in unison from the rows of plastic chairs. "Afraid!"

"Do not be fooled by the parents," Farida continued, speaking into a microphone over the whir of a single ceiling fan. "You have to be smart about this. You have to make them come to the clinic."

Health workers in Depok have recruited respected community figures, in particular Muslim clerics who run Koran reading groups for women, to preach the virtues of vaccination. But Komora Mingsih, 52, one of the volunteers, lamented it might be too late to save this drive.

"I don't think it will succeed," she added, out of earshot of the other volunteers. "Most likely, people are still afraid."

Special correspondent Yayu Yuniar contributed to this report.

Relatives assist Fauziah, 4, who was partially paralyzed by a suspected bout of polio. At least 226 Indonesians have been infected this year.Ebon Sunarti, a former health worker, refused to let her daughter receive a second dose of vaccine.