'These are not true alternatives, only speculative ideas,' said one researcher of the proposed new methods for growing embryonic stem cells. Each idea faces significant scientific or ethical hurdles or both, he said.

The hearing came amid intense political maneuvering surrounding congressional efforts to upend the Bush administration's policy on embryonic stem cells, which restricts federal funding to 22 existing cell families, or lines, created before Aug. 9, 2001.

A bill to expand financing to all available lines, including those created after that date, passed in the House in May and awaits a vote in the Senate. If it passes, President Bush has threatened a veto, which would be his first.

"There is a clear concern we are not moving far enough and fast enough to support this research," said Sen. Arlen Specter, R-Pa., who chaired the Labor, Health and Human Services Subcommittee hearing. Specter mentioned his own battle with cancer at the hearing's outset in calling for more stem cell research.

Specter is the sponsor of the Senate bill, along with subcommittee member Sen. Tom Harkin, D-Iowa. The hearing was held largely to head off opponents who Specter says are embracing stem cell alternatives in an attempt to sap support for his bill.

Embryonic stem cells are the first few hundred cells found in an early embryo. Because they can divide and grow into every type of tissue, researchers have looked to them as a source of transplant tissue to someday treat spinal injury and diseases such as diabetes and cancer. The lines are generally created from early embryos donated for research by fertility clinic patients; the embryos would otherwise be discarded.

However, because creating lines of these cells requires the destruction of early embryos, opponents such as the United States Conference of Catholic Bishops consider the research immoral.

At the hearing, scientists discussed four alternative approaches to creating embryonic stem cell lines that in theory would evade moral objection:

• Use of dormant or "dead" early embryos that stop growing within the first few days after their creation. In theory, their stem cells are still alive.

• Use of an individual cell plucked from an early embryo, keeping it intact, and using it to grow a cell line. Called pre-implantation genetic diagnosis (PGD), it is now used about 1,000 times a year nationwide to diagnose diseases but hasn't generated human cell lines.

• Use of "altered" embryos, with genes scrambled to ensure that they could never grow into human beings.

• Use of adult stem cells "reprogrammed" to act like embryonic cells.

All of the ideas were put forward in a report in May by the President's Council on Bioethics, which detailed ethical and technical problems facing each one. One council member, biologist William Hurlbut of Stanford, testified at the hearing in favor of altered embryos. He called it a technological solution to the embryonic stem cell research debate. "I think there is a moral dilemma," he said.

But others argued that the alternatives, even if worthy of research, did not justify a holdup in expanding cell lines available for federal research grants. "These are not true alternatives, only speculative ideas," said pediatrics researcher George Daley of Children's Hospital in Boston. Each idea faces significant scientific or ethical hurdles or both, he said.

"We need to move forward," said biologist Robert Lanza of Advanced Cell Technology in Worcester, Mass. Lanza described progress in the PGD approach but acknowledged that it could take a decade for it to generate human embryonic stem cells.

Since the isolation of human embryonic stem cells in 1998 by University of Wisconsin researchers, the topic has generated fierce debate and figured in last year's presidential election. Sen. Sam Brownback, R-Kan., a strong opponent of the research, has attributed much of that ferocity to the abortion debate and concern about the use of early embryos for research.

The National Institutes of Health spent $24.3 million last year on embryonic stem cell research.