WASHINGTON — The Senate is having trouble deciding how to approach the controversial issue of stem cell research using human embryos, dimming hopes of Sen. Arlen Specter, R-Pa., and other supporters that a bill will pass before the summer recess begins Friday.

In May, 50 House Republicans defied President Bush's veto threat to help pass a bill that would allow federal funding for research using donated embryos that would otherwise be discarded by fertility clinics. President Bush limited such research to stem cell lines that existed Aug. 9, 2001. He has said he opposes spending taxpayer money “to promote science that destroys life in order to save life.”

Patients' groups and high-profile advocates such as former first lady Nancy Reagan and actor Michael J. Fox say the research could help provide cures for Parkinson's, diabetes and other diseases. A USA TODAY/CNN/Gallup Poll in May found 53% favor easing the restrictions or having no limits on funding, tracking a similar survey last year.

The 238-194 House vote, though short of a veto-proof majority, lent momentum to an identical bill by Specter and Sen. Tom Harkin, D-Iowa. It also put some Republican senators such as Majority Leader Bill Frist and Kay Bailey Hutchison who want to encourage more research — but are reluctant to cross Bush — in a bind.

Frist, R-Tenn., is trying to get Minority Leader Harry Reid, D-Nev., to agree on votes on several bills, and that has left Specter and other supporters frustrated.

“I have grave concerns that the issues (in the different bills) can be crystallized and understood,” Specter said. “We waited long enough.”

He is weighing whether to attach his measure to a must-pass bill paying for operations at the Health and Human Services Department and other federal agencies. If Specter is successful, it would force the Senate into negotiations with the House of Representatives over stem cell research and put Bush in the position of possibly vetoing the health spending bill. Still, the issue may be on hold until September at the earliest while a Supreme Court confirmation hearing, spending bills and other business occupy the Senate.

One analyst says the different bills offer senators some protection. “It looks like an effort to find cover for Republicans who don't want to vote for the House bill but don't want to be out there opposing something that's very popular with most Americans,” said Norman Ornstein, a congressional expert at the American Enterprise Institute, a Washington think tank.

Despite the maneuvering, senators who support the Specter bill defended Frist's management of the issue. Sen. Orrin Hatch, R-Utah, a supporter of embryonic stem cell research, called it “a legitimate attempt to try to give everyone something they can be for.”

There were bills for those who want to end all embryonic stem cell research and for those willing to expand research with some limits:

•Sen. Sam Brownback, R-Kan., who equates destroying an embryo for research with abortion, has drafted a bill that would ban all human cloning, including human embryonic stem cell research.

•Hutchison, R-Texas, usually a reliable Bush vote, offers a compromise that would move the cutoff date for using frozen embryos in research to the day her bill would become law. That would make 400,000 existing embryos eligible to be donated for research. The new deadline “would discourage any possibility of having an industry of creating embryos to destroy them” she said. “It's the best combination of ethical restrictions but one that allows moving forward to do the research.”

Harkin says those opposed to his bill on moral grounds aren't likely to accept Hutchison's. “If (Bush) can accept that, he can accept ours,” Harkin says.

•Frist, Johnny Isakson of Georgia and George Allen of Virginia are among Senate Republicans backing a bill supported by the White House that would fund research that extracted stem cells from human embryos without destroying them. Many scientists, including Harvard's George Daley, a stem cell researcher, say such “alternatives” are unproved and would divert and delay legitimate medical research.

•Hatch has a bill that would fund research to extract stem cells from umbilical cord blood and bone marrow. A similar House measure passed overwhelmingly.

White House spokesman Trent Duffy says Bush wants “to balance the science and ethics” of stem cell research “without using taxpayer money to destroy human embryos.”

American University political scientist James Thurber says Bush hasn't built public support for his position on stem cell research and “may get rolled on this one.”