"This is an attempt to find common ground between science and pro-life," Coleman, R-Minn., said in an interview with The Associated Press.
Four years ago, Mr. Bush banned federal funding for embryonic stem cell research on lines not already developed by Aug. 9, 2001. In essence, Coleman is proposing to move that deadline to today.
"He's drawn a line in the sand that's not pro-science," Coleman said of Mr. Bush. "We don't want to be the party that's anti-science. We're not finding real hope" for cures.
Coleman, who opposes legalized abortion, said his proposal would open up hundreds of stem cell lines to research and possible cures for diseases, and would avoid the moral quandary by using embryos that have already been destroyed.
Stem cells can divide and become any kind of cell in the body. Because harvesting embryonic stem cells destroys embryos, Mr. Bush and many other conservatives equate the process with abortion and view it as immoral. Proponents say the promise that stem cell research holds for treating and curing diseases such as Parkinson's and Alzheimer's outweigh the ethical concerns.
Coleman said that he spoke with the White House about his proposal last week, and the Bush administration opposes it. White House spokesman Allen Abney confirmed that Mr. Bush remains opposed to any proposals that lift the ban.
Coleman said that a lobbyist for the National Right to Life Committee expressed opposition to his proposal, arguing that it will encourage researchers to come back in a couple of years and ask that the deadline be moved yet again.
"I don't buy that," Coleman said. He argued that there are enough stem cell lines available now for researchers to make real breakthroughs.
National Right to Life did not return phone messages left Tuesday.
There are already a half-dozen stem cell bills pending in the Senate, but Coleman argued only his has the chance to get the two-thirds vote necessary to overturn a promised veto from the president on any bill overturning his 2001 restrictions. He said he would reach out to lawmakers during the August recess and introduce the bill in September.
Coleman said his decision to try to find a workable plan was shaped in part by his own experience — two of his four children died of a rare genetic disorder. Those losses also "steeled my sentiment to pro-life," he said.
"This is a stopgap measure," Coleman said. "It moves the ball of science forward."
But Sean Tipton, a spokesman for the Coalition for the Advancement of Medical Research, which supports stem cell research, lumped Coleman's proposal in with Mr. Bush's policy.
"We know from experience that having an arbitrary date results in a failed policy — that's what we have now," Tipton said. "And the reason that policy fails is it locks you into outmoded technology. You're immediately using inferior research materials."
"It's a nonsensical way to make policy," Tipton added. "What do we do, come back next year and say there are better lines today, so let's move the line again?"