Members of the US Congress and executives at the National Institutes of Health said they would act swiftly to turn the new policy into law and into cash for laboratories.

Obama's executive order reversed and repudiated restrictions placed on the research by his predecessor, George W Bush, freeing labs across the country to start working with the valued cells, which give birth to all cells and tissues in the body.

The move made it possible for federally funded researchers to work with human embryonic stem cells from a variety of sources, not just the few batches Bush had approved.

Officials at the National Institutes of Health, who had chafed under the Bush policy, said they would start to draw up new guidelines within the four-month timeline set by Obama.

They said they may start accepting applications for grants before they finish. "The end goal is to ensure responsible and scientifically worthy human stem cell research," said acting NIH deputy director Lawrence Tabak.

Tabak expressed appreciation that Obama had left all scientific questions to the NIH to decide.

The usual process for getting an NIH grant takes about nine months, Tabak said, and the average stem cell grant has totalled about $375,000 a year for five years.

NIH research is the gold standard underlying much other medical research in the United States, with academic labs doing the basic work and then licensing the actual development of treatments to companies.

"By doing this, we will ensure America's continued global leadership in scientific discoveries and technological breakthroughs," Obama told a packed White House ceremony.

Shares of stem cell leader Geron Inc, which won government permission in January to test embryonic stem cells in human patients, closed up 16 per cent at $4.51. Shares in other stem cell companies also soared.

MAKING LAW

Researchers said companies that have been afraid to test the waters will likely leap in now that federal dollars can be used for the most risky and experimental basic research.

Diana DeGette and Mike Castle, two members of Congress who pushed legislation to bypass the Bush restrictions, said they would press to turn Obama's decision into legislation.

"Mike and I both feel that our immediate and top priority is to codify the executive order and pass the legislation that we have passed twice before and that was vetoed by President Bush twice," DeGette, a Colorado Democrat, told reporters. "Our legislation is already prepared and introduced."

But DeGette and Castle, a Delaware Republican, said they would not take on the Dickey-Wicker amendment, which prevents the use of federal funds to actually extract the stem cells from human embryos.

"I think the Dickey-Wicker decision perhaps could be done later," Castle said.

Not everyone was happy. "Obama opens door to human embryo farms", the National Right to Life Committee said in a statement.

"If an embryo is a life, and I believe strongly that it is life, then no government has the right to sanction their destruction for research purposes," said Kansas Senator Sam Brownback.

Michael Werner of the Coalition for the Advancement of Medical Research, an advocacy group, said states such as California and New York that had established their own stem cell research groups stood to gain from the change.