In size and scope, no initiative on any ballot this year comes close to California's Proposition 71.

Crafted by a group of parents, scientists, Hollywood stars and venture capitalists, the proposal to spend $3 billion on embryonic stem cell research is a virtual end-run around the Bush administration that would put this huge state far ahead of most other nations in a promising -- and controversial -- new field of medicine.

While President Bush and his Democratic rival, John F. Kerry, squabble over whether to invest $25 million or $100 million of federal money in the field, Californians are considering a radically different course. In defiance of Bush's limited national policy, Californians are being asked to pour 10 times as much money into a state program, letting voters for the first time decide whether to invest tax dollars in a specific type of research.

If approved, supporters say the bond measure would revolutionize the fledgling science -- with California and its legions of academic laboratories and biotech firms at the epicenter. The payoff, proponents say, could be treatments for chronic conditions such as diabetes, Parkinson's disease and spinal cord injury.

But the price is high, opponents counter, in both financial and moral terms. To pursue those treatments, scientists must destroy 5-day-old embryos, a process Roman Catholic leaders here call a "direct attack on innocent human life." Payments on the bonds would cost the state nearly $6 billion over 30 years, a sum many say California cannot afford.

The creators of Proposition 71 have assembled a powerful cast of advocates -- from Republican Gov. Arnold Schwarzenegger to Nobel Prize winners, from the head of the Bush administration's stem cell task force to the late actor Christopher Reeve, who appears in a commercial taped shortly before his death. Other supporters include the California Chamber of Commerce, actor Michael J. Fox, who has Parkinson's, and George P. Shultz, secretary of state under President Ronald Reagan.

On the other side is a collection of unlikely allies -- feminists who fear the demand for embryos will create "egg farms," fiscal conservatives and evangelical Christians. They are short on famous names and even shorter on cash.

Although national polls show more than 70 percent of Americans endorse embryonic stem cell research, recent state polling puts support for the bond proposal at about 50 percent. By historical standards, that would not bode well for passage because late-deciding voters tend to oppose initiatives, but a deluge of pro-initiative ads could tip the balance.

"The fact that this is on the ballot at all is a stunning testimonial to the power of citizen advocacy," said Mary Woolley, president of the nonpartisan Research America, which promotes public investment in science.

Yet what Woolley and proponents hail as democracy in its purest form, others see as an abuse of the electoral process -- a small, well-funded constituency using emotion to sell expensive, unproven science. "This is taking billions of dollars from desperately needed health care to support this science project," said H. Rex Greene, medical director of the cancer center at Mills-Peninsula Health Services in San Mateo. "If this ever leads to cures, it will be decades away -- if ever."

Proposition 71 was born out of frustration, hope and, detractors would say, greed.

It started here in the shadow of Stanford University, in the nondescript office where Bob Klein has made millions as a real estate developer and where he drafted the initiative.

"I have a 14-year-old son with diabetes, and my 87-year-old mother is dying of Alzheimer's," said Klein, seated at a conference table strewn with legal pads, cell phones, tissues and packets of vitamins -- telltale signs of the final days of an exhausting campaign. "I see a tremendous amount of suffering at both ends of the age spectrum."

To patients and families, embryonic stem cells offer a spark of hope. They speak in urgent tones of not having time to waste on political haggling. Scientists are enthusiastic about cells taken from embryos because they have the unique ability to morph into almost any type of tissue or cell, potentially replacing diseased or damaged tissue with healthy, self-renewing replacements, in some cases grown from a patient's own cells.

To date, researchers mostly used "spare" frozen embryos that would otherwise have been discarded by fertility clinics. Proposition 71 would allow California scientists to use state funds to work with such embryos or to create new ones in a laboratory in a process called nuclear transfer technology, or therapeutic cloning.

In August 2001, Bush decided to limit federal support to only the cell colonies, or "lines," that had been harvested -- touted to be more than 60 at the time, but in reality just a couple dozen viable lines. His compromise reflected an attempt to balance "good science with good ethics," he said recently.

Lynn Fielder, a 42-year-old mother who takes half a dozen pills every three hours to manage her Parkinson's, sees the ethical dilemma differently. "It would be absolutely irresponsible to not be pursuing something like this," she said. "What can be more moral than saving the lives of people who exist and easing the burden on their families?"

Researchers complain that the Bush policy, and proposed GOP legislation to criminalize treatments using embryonic stem cells, has put a chilling effect on the scientific community.

"I got into this because I really see a threat, particularly when it is based on ideology or religion," said Paul Berg, a Nobel winner at Stanford. "Proposition 71 is our way of saying, 'We're not gonna take it any more.' We have the wherewithal, and the citizenry is backing us to move forward with this opportunity."

A few other states have passed "safe harbor" legislation allowing embryonic stem cell research, and New Jersey is poised to spend $5 million a year on it, but none approaches the ambition of the California measure. Klein designed the bond proposal so that the state would not make payments for the first five years, an approach that helped sway Schwarzenegger.

With Klein's $2.5 million as seed money, the group Cures for California has raised more than $24 million, with large checks from wealthy donors such as Microsoft chief executive Bill Gates and Sen. Jon S. Corzine (D-N.J.), advocacy groups such as the Juvenile Diabetes Research Foundation, and numerous venture capitalists.

Opponents, who have raised less than $200,000, describe those donations as a thinly veiled financial grab by special interests. "A group of venture capitalists spent about $5 million to access $6 billion in taxpayer money," said Tom Bordonaro, a former state lawmaker who has had to use a wheelchair since a car accident 27 years ago. "That's a pretty good return on investment."

The California Catholic Conference has distributed "homily notes" for every Sunday in October, detailing arguments against the initiative. The notes draw analogies to abortion, urging parishioners to defend "innocent life" by voting no.

The umbrella group Doctors, Patients and Taxpayers for Fiscal Responsibility, focused on fiscal issues. It calls the initiative "a blatant taxpayer rip-off that lines the pockets of a few large biomedical corporations" at a time when the state is "teetering on the edge of bankruptcy."

This weekend, on television sets across the state, Reeve delivers the final appeal for the initiative. The spot is introduced with a message from his family explaining they "wished to honor his memory by airing this, his last recorded message." From his wheelchair, the paralyzed actor urges: "Please support Prop. 71 -- and stand up for those who can't."

About 3,000 miles away, on the Bethesda campus of the National Institutes of Health, views are mixed. James Battey, chair of the NIH stem cell task force, is an enthusiastic supporter who says Proposition 71 could "transform" stem cell research.

NIH Director Elias A. Zerhouni, taking pains to note he was not present when Bush devised his stem cell policy, said the initiative could "complement" his agency's work, but he offered a cautionary note about voters setting research priorities.

"You can see what is politically attractive can take precedence over what's important from the standpoint of public health," he said. "In the long run, I don't think the nation should make decisions in that manner."

A TV ad in which the late Christopher Reeve urges voters to "stand up for those who can't" is part of a campaign including many celebrity backers.Gov. Arnold Schwarzenegger (R) supports Proposition 71.