NEW DELHI, India -- Health workers in India knocked on millions of doors Sunday in a campaign to vaccinate 165 million of the country's children against polio this year -- the largest immunization drive ever against the disease.

The workers, who themselves numbered in the hundreds of thousands, hoped to reach 98 million children in 10 Indian states on Sunday alone, said Savita Varde Naqwi, a spokeswoman for UNICEF. Other rounds were planned for later this year, she said.

They traveled to remote villages and urban slums where the virus is easily spread due to crowded conditions and poor sanitation. Teams of health workers also visited airports, and railroad and bus stations.

The main target was Uttar Pradesh, India's largest state, which accounted for 66 percent of the 1,556 new polio cases found last year, Naqwi said. Six of every 10 Indian children under 5 -- the age group most vulnerable to the disease -- live in the state.

Polio strikes the central nervous system, causing paralysis and sometimes death. It is transmitted through food or water contaminated by the feces of an infected person.

Once a major problem, the disease has disappeared from much of the planet and the World Health Organization hopes to eradicate it completely by 2005. But an alarming increase in cases in Uttar Pradesh has prevented the U.N. agency from reaching that goal, officials said.

"Nearly two-thirds of all the polio cases worldwide are found right here, in Uttar Pradesh," said Gro Harlem Brundtland, the WHO's director-general. He spoke to reporters in Lucknow, the state's capital, during a visit aimed at boosting the anti-polio campaign.

India's inability to contain the disease stems from a number of factors, including a lack of interest among parents and officials and ineffective vaccines provided by the government, critics say.

"Officials and doctors will have to think about why children, who had been brought under the polio coverage umbrella, fall prey to this dreaded disease," Uttar Pradesh Health Minister Phagu Chauhan told The Associated Press.

Muslims, India's largest minority, have also resisted the campaign, fearing that the vaccines are part of a government plan to limit the Muslim population in this Hindu-majority nation.

"There is a myth among Muslims that polio vaccine turns children impotent. This false propaganda is keeping the Muslims away from the polio booths," said Girish Chandra Chaturvedi, a senior Uttar Pradesh health official.

On Sunday, helicopters dropped pamphlets in predominantly Muslim areas urging parents to take their children to the nearest polio centers, saying their fears about the vaccines were unfounded.

This story appeared in The Daily Herald on page A7.