ASHINGTON, Sept. 25 — A parade of frustrated scientists told a Senate subcommittee today that research on human embryonic stem cells was moving exceedingly slowly because of the severe restrictions that President Bush has imposed on federal financing for the work.

"The field of human embryonic stem cell research is in a fragile state at best under the current presidential policy," said Dr. George Q. Daley of the Whitehead Institute in Boston, adding that the policy "threatens to starve the field at a time when greater nourishment is critical."

Dr. Daley, who has used stem cells to cure mice of the immune deficiency known as "bubble boy disease," was one of several scientists who recounted the tribulations of trying to obtain the cells Mr. Bush promised them in August 2001.

Scientists contend that embryonic stem cells, which can form any of the body's cell types, will one day be used to treat many diseases. But researchers must destroy human embryos to get the cells, and that is why Mr. Bush restricted federal financing to just the cell colonies that had been identified at the time of his announcement.

The National Institutes of Health says there are 78 self-sustaining cell colonies, called lines, that researchers may work on. The new director of the institutes, Dr. Elias Zerhouni, told lawmakers today that he had set up a task force to help get those lines into the hands of researchers.

But the scientists, while praising Dr. Zerhouni, said that despite his efforts the vast majority of the lines were not currently available. That is partly because some of the cells are not fully developed and partly because researchers must go through painstaking negotiations to persuade the companies and universities that own the lines to share them.

Dr. Curt Civin, a stem cell researcher at Johns Hopkins University, said he had spent months negotiating with an Indian company that owns seven approved lines only to have his agreement canceled in May when the Indian government put a hold on all stem cell shipments.

Dr. Civin then paid $5,000 — 50 to 100 times the fee for ordinary cells, he said — for a line from the University of Wisconsin. But "technical problems" with the cells have kept him from receiving them, he said. Dr. Civin has received some private money for his work, but the foundation that gave him the grant, following the federal lead, has insisted that he use only the lines approved by the N.I.H.

"Embryonic stem cell research is crawling like a caterpillar," Dr. Civin told the committee. The cells, he said, are available "only to those persistent and patient enough to jump through a series of hoops and endure lengthy waits."

The tales of researchers' experiences prompted Senator Arlen Specter, the Pennsylvania Republican who is chairman of the hearing, to say later that he would press Congress to expand the president's policy.

"I think the time has come," Mr. Specter said, "to legislate in the field."

Whether Mr. Specter has the political support to do that is unclear. Legislation to authorize so-called therapeutic cloning, a type of stem cell research that also involves the destruction of embryos, is stalled in the Senate, and Mr. Specter acknowledged today that he would need to talk to his colleagues before proposing another bill.

At least one state, California, is trying to encourage the research. Over the weekend, Gov. Gray Davis signed a bill explicitly authorizing human embryonic stem cell research. The bill, which requires the studies to be regulated, is mostly symbolic because it does not override the president's policy on federal financing and does not set aside any new money for the research.

Several researchers argued today that the National Institutes of Health should set up a repository of stem cells that all scientists could draw on. One researcher, Dr. Gerald Schatten of the University of Pittsburgh, said he feared that without enthusiastic support from the federal government, work would proceed so slowly that the public would grow frustrated and taxpayer support would dry up.

"If we're going to do this, let's do it," Dr. Schatten said. "We didn't go to the moon and decide to come back one-third of the way."