NEW DELHI (Reuters) - Microsoft founder Bill Gates on Wednesday said he was worried the global financial crisis he says could last two to three years might drive rich countries to cut back spending on health aid for the developing world.

Echoing comments made last week by U.N. chief Ban Ki-Moon, the billionaire philanthropist said the world's poorest people will suffer the most during the economic slowdown, and said a "strong voice" was needed to keep them a global priority.

"We certainly are concerned that some of the rich world governments could either reduce their increase or even cut back the amount they spend on these issues," Gates said in India's capital.

"We have to admit that getting that generosity gets even more challenging when there's tough economic times."

Gates said he expected the United States to undergo a period of "economic contraction" for two to three years as a result of a meltdown in the housing market and heavy consumer debt.

Gates was optimistic about the newly elected American president Barack Obama's efforts to tackle global health issues, saying Obama has "shown a lot of interest" and would "drive improvements in those areas."

Gates is on a visit to India on behalf of his charitable foundation to tackle health issues, focusing on polio eradication and fighting HIV/AIDS.

Meeting with Indian health officials and polio experts, Gates said he was confident polio can be successfully eradicated with India leading the way.

Gates called for increased government spending on health and urged Indian health officials to consider using innovative approaches such as injection vaccines to tackle the crippling disease.

While a lot more expensive and trickier to administer, the injected IPV vaccine could be used in addition to oral vaccines to stop the spread of polio in high-risk areas.

Oral vaccines have not proven to be as effective in India as elsewhere, a problem which some researchers suspect is down to poor sanitation and a higher presence of other diseases that stop the vaccine working properly.

A world effort to beat polio has succeeded in slashing the number of cases by 99 percent over the past two decades, but the disease is still endemic in India, Pakistan, Afghanistan and Nigeria.

The Bill and Melinda Gates Foundation has committed more than $17 billion in grants since it began in 1994, and has given hundreds of millions of dollars in a global campaign to eradicate polio.

(Editing by Alistair Scrutton and Sanjeev Miglani)

© Thomson Reuters 2008 All rights reserved