Most Americans do not want to live beyond age 100, and a poll out Tuesday suggests many worry that anti-aging technologies may end up being a luxury for the rich.

The survey of more than 2,000 people by the Pew Research Center's Religion and Public Life Project sought to probe the nation's views on the prospect of living longer lives.

Already, aging adults account for a growing share of the US population. About 41 million Americans are 65 or older, making up 13 percent of the population, up from four percent in 1900.

By 2050, that number will rise to 20 percent, according to Census Bureau projections.

A majority of US adults (56 percent) said they would not "choose to undergo medical treatments to slow the aging process and live to be 120 or more," said the Pew report. A total of 38 percent said they would.

With the average US life expectancy at 78.7 years, more than two thirds said they would like to live longer than that, somewhere between 79 and 100.

The median, or midpoint, for ideal lifespan was 90, or about 11 years longer than the current US average.

Asked whether current medical treatments are worth the costs because they help people live longer and better quality lives, 54 percent agreed and 41 percent disagreed on grounds that modern medical advances "often create as many problems as they solve."

There was also significant concern about how life-extending technologies would be used, and by whom.

Seventy-nine percent said everyone should be able to get medical treatments that would slow, stop or reverse the aging process.

However, two-thirds said that in practice, only the wealthy would have access.

Two-thirds of respondents also said that longer life expectancies would strain natural resources, and believed that "medical scientists would offer the treatment before they fully understood how it affects people's health."

Views were split on the question of whether the economy would be more productive if people could work longer -- with 44 percent agreeing and 53 percent rejecting this idea.

For certain health issues, Americans were optimistic that medical science would perform well in the future. Seven in 10 said that they expect a cure for most cancers by 2050, and 71 percent said artificial arms and legs will perform better than natural ones.

"And, on balance, the public tends to view medical advances that are available today to prolong life as good (63%) rather than as interfering with the natural cycle of life (32%)," the survey said.

By 2050, the government forecasts there will be at least 400,000 Americans aged 100 or older.

Just 10 percent said the trend toward an aging population is a bad thing.

One quarter said a major anti-aging breakthrough that would allow average folk to live to 120 and beyond was likely by 2050.

The telephone poll was conducted from March 21 to April 8 among a nationally representative sample of 2,012 adults and carried a margin of error of plus or minus 2.9 percentage points.

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