WASHINGTON – Senate supporters of embryonic stem cell research refused to take another no for an answer Tuesday, advancing politically popular legislation that is assured of passage, yet doomed for the second straight year to a veto that Congress cannot override.

“This bill eventually will become law,” vowed Sen. Dianne Feinstein, D-Calif., as debate opened on a bill to loosen federal funding restrictions on research that supporters say offers hope for treatment of numerous diseases. “If not this year, then next year. If not next year, then the following year.”

Assuredly not this year.

President Bush, who cast the only veto of his tenure on a stem cell bill in 2006, quickly made it clear this year will be no different. The bill “would use federal taxpayer dollars to support and encourage the destruction of human life for research,” the White House said in a written statement.

Stem cells are created in the first days after conception, and are typically culled from frozen embryos, which are destroyed in the process.

The legislation would overturn a policy Bush established in 2001, when he said federal funds may only be used for research on a limited number of stem cell lines that were in existence before the day of his announcement. The administration’s goal was to satisfy calls for funding of scientific research without offending anti-abortion conservatives who had helped elect him to the White House.

The bill’s supporters concede they are short of the votes needed to override a veto, but appeared eager to confront the president again on an issue with strong public backing.

Republican opponents backed an alternative they said offered hope for scientific progress without destroying human embryos, a sticking point for conservatives.

In the Senate, supporters were quick to respond to any implication that their measure was unethical

Sen. Tom Harkin of Iowa, the bill’s chief sponsor, said 50,000 children were born last year to couples using in vitro fertilization. “Obviously there are some embryos left over. They would like to be able to donate those for research because they’re not going to have any more children,” he said.

“So it seems to me the ethics of this are, are you just going to discard those, or would it be more ethical to use them to save lives.”

Sen. Susan Collins, R-Maine, agreed. The leftover cells are “discarded every day, every month, every year as medical waste. How much more life enhancing it would be to use them for research that would save lives, that could preserve lives, that would prolong lives,” she said.