Religious groups oppose the scientific work in which culling of stem cells kills embryos, equating that with abortion, and had urged Bush not to be the first president to fund the research -- even with limits.
Proponents of the science, including Ronald Reagan's widow, Nancy, and 58 Democrats and Republicans in the Senate say it could lead to cures to diseases such as diabetes and Alzheimer's.
Ronald Reagan suffered from the latter for a decade before his death June 5 due to related pneumonia.
Only a fraction of the initial 78 stem cell lines -- 21 at last count -- are yet available to researchers because of problems with the lines' growth or their ownership.
In March, a National Institutes of Health count cast doubt on how many ultimately would be usable.
Proponents say more than 100 new cell lines have been created worldwide since Bush's decision -- some with new techniques that may make them more scientifically useful -- and could be studied under more open rules. An exact count is not possible because private funding means much of the work is done without public scrutiny.
With polls indicating overwhelming support for the research, Kerry has promised to give scientists more freedom. He has described Bush's actions as a ban when what the president has done is limit the research.
''That's so ridiculous," Laura Bush said in an interview. ''It's one of the myths that start during a campaign."
Kerry spokesman Phil Singer said Bush's restrictions apply to 99.9 percent of potential stem cell lines that could be studied. ''If that's not a ban," he said, ''we don't know what is."
Laura Bush said Kerry was trying to make a political issue out of her husband's policy ''without saying what's right. I imagine he knows better."
Like others campaigning for the GOP ticket, Bush credited her husband with being the first president to use taxpayer money for the research. That is true, perhaps only because the science is so new. The policy of Bush's Democratic predecessor, Bill Clinton, allowed taxpayer money to be used in the research of any stem cell lines, but he never funded the nascent research. Bush invested $25 million in limited research.
