India has only about 2.5 million people infected with H.I.V., less than half of previous estimates, the Indian health minister and United Nations health officials said yesterday.

As a result, instead of having an estimated 5.7 million cases, the most in the world, India is now in third place, behind South Africa, with 5.5 million, and Nigeria, with 2.9 million.

In the past, India was accused by many global AIDS officials of denying its epidemic and doing too little to prevent it. Now some Indian political figures and American epidemiologists have been vindicated.

However, the health minister, Dr. Anbumani Ramadoss, was quick to say that the threat, while smaller, was still serious.

''In terms of human lives affected, the number is still large, in fact very large,'' Dr. Ramadoss said at a news conference in New Delhi, Reuters reported. ''This is very worrying for us.''

The estimate was revised downward, the United Nations AIDS program, Unaids, said, because of a national survey, including blood samples, of more than 100,000 people taken in 2005 and 2006. Called the National Family Health Survey III, it was paid for largely by the United States Agency for International Development.

Previous estimates had been based on blood samples taken from women visiting prenatal clinics, patients at sexually transmitted disease clinics and small samplings in high-risk groups like prostitutes, truckers, intravenous drug users and gay men.

But the mathematical models inflated nationwide prevalence rates because there were few samples from men, rural dwellers, the middle class and people outside industrialized southern India and the Myanmar border, where the disease is concentrated.

The new survey suggests that India's epidemic is more like that in the United States, concentrated in high-risk groups, rather than like the generalized epidemics in southern Africa.