"This order is an important step in advancing the cause of science in America," Obama said in the East Room of the White House.

He said he would not only open the door to this medical research, but also would unleash all forms of science in areas such as the environment from what he believes were limits imposed by the Bush administration rooted in conservative ideology, politics and religion.

"Promoting science isn't just about providing resources," Obama said. "It is about letting scientists ... do their jobs, free from manipulation or coercion, and listening to what they tell us, even when it's inconvenient; especially when it's inconvenient. It is about ensuring that scientific data is never distorted or concealed to serve a political agenda, and that we make scientific decisions based on facts, not ideology."

Obama's order lifted all of President George W. Bush's restrictions on research into stem cells, which can replicate indefinitely and differentiate into many cell types, and it allows "scientifically worthy human stem-cell research including human embryonic stem-cell research." He gave the National Institutes of Health 120 days to prepare guidelines on how the research will be financed and conducted.

In addition to signing an executive order allowing financing of stem cell research, Obama signed a memo ordering a "strategy for restoring scientific integrity to government decision making."

The reversal is the latest in a periodic struggle between science and religion or ideology. It's one that dates as far back as Galileo's clashes with the Roman Catholic Church and Darwin's theory of human evolution, and extends through the struggles over abortion during the past several decades.

"There are moments when religions and science have clashed," said David Masci, a senior research fellow at the Pew Research Center's Forum on Religion & Public Life. "One area where they clash is when science says something that conflicts with religious truths. Evolution is one example. The other is when people feel like science has taken a step too far."

Those tensions were exacerbated over the past several years, a period when candidate Obama joined a chorus of critics complaining that the Bush administration ignored science on issues such as global warming. "We need to end the Bush administration's war on science, where ideology trumps scientific inquiry and politics replaces expert opinion," he said during the campaign.

Among the flash points between science and ideology or religion during the Bush years:

-Republicans rejected calls to limit emissions widely thought to cause global warming.