At least three for-profit companies are racing to develop large amounts of embryonic stem cells even as President Bush struggles to decide whether the government should hinder such research.

The stem cells hold the potential to cure diseases and ailments from cancer to spinal cord injuries. If this dream can be realized, these companies stand to reap millions — if not billions — in profits.

Each company employs different but still controversial techniques to harvest embryonic stem cells. One buys leftover embryos from fertility clinics. Another is working to create embryos by way of a cloning method similar to the one used to make Dolly the sheep. The third pays men and women for their sperm and eggs, then creates embryos in the laboratory.

Each company's research involves plucking the coveted stem cells from 4- or 5-day-old human embryos, which must be destroyed in the process.

Anti-abortion activists and others consider all three techniques unethical, saying they result in the destruction of human life.

Proponents of such research argue that these days-old, undifferentiated cells cannot be viewed as human, and they stress that they have no intention of implanting them in a womb and producing babies.

Since 1996, federal law has banned the use of tax dollars for research that destroys embryos. The Clinton administration decided federal money could pay for research as long as the stem cells were extracted with private money.

Bush, who has come under pressure to reverse the Clinton policy and disallow any federal money for human embryonic stem cell research, appears to be searching for a compromise -- possibly adopting a middle ground that imposes new restrictions but allows the research to move forward.

"The work will go on, one way or another," said Thomas Okarma, chief executive of Menlo Park-based Geron Inc., which funded the two scientists who first isolated human stem cells in 1998 and still dominates the field.

 Geronbuys leftover frozen embryos from fertility clinics and cracks them open to obtain the stem cells. Geron owns the worldwide rights to this process and has filed about 30 new patent applications for the various techniques and technology it uses.

Chief executive Thomas Okarma said he considers Geron's technique ethically sound.

"These things aren't people," he said. "These are all frozen excess and no longer needed by the couple. And they are either going to be thrown away or stored forever."

Eventually, Geron hopes to get stem cells without having to use embryos at all. It hopes to do this by finding and cloning the proteins in eggs that lead to the creation of stem cells. Then, Okarma said, "living cells will be tomorrow's pharmaceuticals."

Across the country in Worcester, Mass., Advanced Cell Technology is working on another technique that it hopes will enable it to generate stem cells by growing human embryos without the use of sperm.

Advanced Cell's plan is to pay women to take fertility drugs to produce excess eggs. Researchers would then take an egg, remove its nucleus and genetic material and fuse it with a skin cell containing adult genetic material. With a jolt of electricity, the researchers then would coax the egg to replicate as if it had been fertilized with sperm. After a few days, stem cells would be ready for harvesting.

So far, Advanced Cell has yet to obtain a stem cell with this technique. Chief executive Michael West, a Geron co-founder who left for Advanced Cell last year, said the company has not yet created embryos.

Many scientists consider the results of Advanced Cell's technique to be human embryos, since theoretically, they could be implanted into a womb and grown into a fetus. West himself has used the term "embryo." However, his ethical advisers prefer terms such as "ovumsum."

"These are not embryos," said the chairman of Advanced Cell's ethics advisory board, Dartmouth University religion professor Ronald Green. "They are not the result of fertilization and there is no intent to implant these in women and grow them."

A third effort was announced this week by the Jones Institute for Reproductive Medicine, a private fertility clinic in Norfolk, Va., that was responsible for the birth in 1981 of the nation's first test-tube baby.

The American Society for Reproductive Medicine said it believes the researchers there are the first in the United States to have created embryos expressly for stem cell research, using eggs and sperm from paid, consenting adults.

"At one level, it's cleaner" ethically than using leftover embryos, society spokesman Sean Tipton said. "There's no question what you're going to do with these embryos. You're going to the individuals up front."

Only the Geron-generated cells would be eligible for federally funded research dollars under the Clinton administration guidelines, which called for using only surplus embryos from fertility clinics. The Advanced Cell and Jones Institute embryos would not pass this federal test.