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Silicon Valley tycoons, Nobel laureates and Hollywood celebrities are backing a measure on California's Nov. 2 ballot to devote $3 billion to human embryonic stem cell (search) experiments in what would be the biggest-ever state-supported scientific research program in the country.

The measure — designed to get around the Bush administration's restrictions on the funding of such research — would put California at the very forefront of the field. It would dwarf all current stem cell projects in the United States, whether privately or publicly financed.

Proposition 71 promises to be one of the most contentious election issues in California, pitting scientists, sympathetic patients who could benefit from stem cells and biotechnology interests against the Roman Catholic Church (search) and conservatives opposed to the research because it involves destroying days-old embryos and cloning.

What's more, cell research has emerged as a major campaign issue between President Bush (search) and John Kerry (search), who promises if elected to reverse Bush's 2001 policy restricting federal funding of such experiments to only those cell lines already in existence.

The measure would authorize the state to sell $3 billion in bonds and then dispense nearly $300 million a year for 10 years to researchers for human embryonic stem cell experiments, including cloning projects intended solely for research purposes. It bans the funding of cloning to create babies.

The amount of money involved far exceeds the $25 million the federal government doled out last year for such research and surpassed even Kerry's promise to expand funding to $100 million annually.

Many scientists believe stem cells hold vast promise for treating an array of diseases from diabetes to Parkinson's. Stem cells can potentially grow into any type of human tissue and scientists hope to be able to direct the blank cells to grow into specific cell types needed for transplant.

Stem cells are harvested from embryos, which are destroyed in the process. They were first discovered in 1997 and even the research's most enthusiastic supporters acknowledge that medicines created with stem cells are still many years away.

Some 22 Nobel laureates and many other scientists support Proposition 71 as a way to get around the Bush administration restrictions. They complain that the political climate has brought the field to a virtual standstill in the United States.

Many expect Proposition 71 to instantly breathe new life into the field while also boosting California's biotechnology industry.

"Stem cell-based therapies have the potential to alleviate suffering for millions of Americans," said Leonard Zon, president of the International Society for Stem Cell Research. "If this proposition is accepted, it will place California at the forefront of stem cell research and therapies."

The vote could be close: An independent poll released Aug. 15 found that 45 percent of 534 likely voters questioned were in favor of the measure, 42 percent were opposed and 13 percent undecided.

The pro-Proposition 71 side has raised far more money than the anti camp: more than $12 million versus just $15,000, according to campaign finance records filed this week.

Among those bankrolling the measure is Bill Gates, who contributed $400,000 on Monday. Silicon Valley tycoons such as Google investor John Doerr and eBay founder Pierre Omidyar have donated millions.

Real estate developer Robert Klein II has donated $2 million. Klein's son suffers from juvenile diabetes.

Several prominent Republicans have also endorsed the research, most notably former first lady Nancy Reagan. Also, millionaire developer Thomas Coleman, a regular contributor to GOP candidates, has donated $378,000. Coleman's daughter has diabetes.

The measure has also been endorsed by actors Michael J. Fox, who has Parkinson's, and Christopher Reeve, who was paralyzed in a riding accident.

Opponents of Proposition 71 concede they will be fortunate if they raise $1 million by November. They said they will have to wage a small-scale campaign even as the pro-Proposition 71 side prepares to open a TV advertising blitz.

"This is something that was put on the ballot by venture capitalists and people who stand to benefit," said opposition campaign manager Wayne Johnson. "The more voters find out about this measure, the more they'll turn against it."

State budget hawks, including the California Republican Party, oppose the measure because it would sink the state deeper into debt.

Gov. Arnold Schwarzenegger has not taken a position on Proposition 71, and many predict he will not do so. Schwarzenegger has said he supports human embryonic stem cell research, but he has also vowed to stop California's slide into debt.