With prospects dimming for a simple Senate vote on a bill to loosen President Bush's restrictions on human embryonic stem cell research, Sen. Arlen Specter (R-Pa.) threatened yesterday to circumvent the political logjam by attaching the wording to the appropriations bill for the Department of Health and Human Services.

"I don't like to put it on an appropriations bill, but we waited long enough," a frustrated Specter told reporters in the Capitol. The strategy, he said, is a "fall-back position which I have avoided up 'til now."

Specter is a lead sponsor of a bill, passed by the House in May, that would allow taxpayer dollars to be used to conduct research on medically promising stem cells derived from embryos that are destined to be discarded by fertility clinics. Such cells are off-limits to federally funded scientists under the policy Bush set in 2001. The bill, which polls indicate has broad support and has been considered sure to pass in the Senate, could trigger a showdown with Bush, who has promised a veto.

Although Senate Majority Leader Bill Frist (R-Tenn.) promised months ago to bring the Senate version to the floor, the field has become muddied by the filing of at least six competing bills that would restrict embryo research in various ways. Senators on both sides of the aisle have been unable to agree on which should be brought to the floor and under what terms.

As chairman of the subcommittee overseeing HHS appropriations, Specter said he was in a position -- in consultation with other senators -- to add the stalled bill as an amendment.

Frist spokeswoman Amy Call suggested the prospects for a vote are not dead. "We keep working for a discrete and clear debate and vote on the House bill and other ideas in this sphere," she wrote in an e-mail.