“None of this work lessens the imperative to loosen federal and state restrictions that currently slow progress in this area,” said Dr. Sean J. Morrison, director of the Center for Stem Cell Biology at the University of Michigan.

While lawmakers who support more federal financing of embryonic stem cell research also hailed the research development, they said such advances should not stop Congress from expanding research that could lead to treatments for a litany of diseases, including Alzheimer’s and juvenile diabetes.

“We welcome these advances as we welcome all advances in ethical life-saving research,” said Representative Diana L. DeGette, a Colorado Democrat and a sponsor of the bill. “However, this new scientific research should not be used as an excuse to say that it is a substitute for embryonic stem cell research.”

Many scientists agree, saying they need to generate new lines of embryonic cells from discarded human blastocysts, or very early embryos. They also want to develop embryonic stem cells by nuclear transfer, the replacement of an egg nucleus with one from an adult cell. A major benefit of nuclear transfer would be to walk a patient’s cell back to an embryonic state so disease processes could be better understood.

“I would find it immoral to delay the research to see if egg nuclear transfer or this method gets to our goals first,” said Dr. Irving L. Weissman, a Stanford University researcher, referring to the new technique.

Democrats urged the president to change his mind and sign the legislation. Their campaign to override the expected veto began only hours after the bill was passed, with Ms. Pelosi and Senator Harry Reid of Nevada, the majority leader, staging a ceremony to send the legislation to Mr. Bush. They invited a few dozen children and adults — many of them in wheelchairs — who say they could benefit from stem cell research.

Any effort to override a veto would begin in the Senate, where the bill passed April 11 on a 63-34 vote. Even counting the three Senate Democrats who were not present for the vote, passage was one vote shy of the two-thirds majority needed to override a veto.