John F. Kerry charged Monday that President Bush has "turned his back on science" in limiting embryonic stem cell research financed by the federal government.

The Kerry campaign rolled out a television ad on the subject, saying that "millions of lives" are at stake, as the Democratic presidential nominee was joined by actor and activist Michael J. Fox at a town-hall-style meeting here.

"It's time to lift the political barriers blocking the stem cell research that could treat or cure diseases like Parkinson's," the ad says. "I believe that science can bring hope to our families."

Joined by Fox, who has Parkinson's disease, the senator from Massachusetts listened as people expressed their hopes that stem cell research could lead to cures for their afflictions. "We stand at the next frontier, but instead of leading the way, we're stuck on the sidelines," Kerry said. The president, he said, is "unwilling to change course."

The stem cell dispute follows Bush's 2001 decision to limit federal funding for such research to the "lines" of cells already in existence, citing moral concerns about the destruction of new embryos. Federal health officials say that just 19 stem cell lines, about one-quarter of what was originally estimated by the White House, have been available for research.

Bush campaign officials accused Kerry -- and many media outlets -- of inaccurately describing the president's decision as a ban on such research, although the ad does not use that word. They note that Bush is the first president to provide funding for the research, which became medically feasible only in recent years. "John Kerry's attacks on stem cell research are trying to mislead the American people by implying a ban that doesn't exist," spokesman Steve Schmidt said.

The invited New Hampshire crowd became emotional when a father, on stage with his diabetic son, held a large package of needles to show how many insulin injections the boy must have in a month.

"The majority of the American people support stem cell research, and it's high time we had a president of the United States who does, too," Kerry said. "We can't afford any more stubborn refusal to face the facts." Fox said of Bush's restrictions: "It was kind of like he gave us a car and no gas."

Kerry's pollster, Mark Mellman, found in a July survey that 69 percent of those questioned favored stem cell research. The support cut across party lines, with 77 percent of Democrats, 67 percent of independents and 60 percent of Republicans in favor of using discarded embryos for the research. Other polls have produced similar findings.

"It's an issue where it's very clear that George Bush is on the wrong side as far as a majority of the American people is concerned," Mellman said. He said that "ideological blinders are preventing Bush from attempting research into treatments for deadly and debilitating diseases." Scientists caution that years of research could be required to make progress against such diseases as Alzheimer's and Parkinson's.

The National Right to Life Committee called the ad "misleading," noting that 53 percent of those questioned in a poll for the organization opposed stem cell research "that requires the killing of human embryos." Advocates say researchers would use embryos that are going to be discarded anyway.

In recent months, 206 House members, 58 senators and former first lady Nancy Reagan, whose husband, Ronald Reagan, died this year of Alzheimer's, have called for an expansion of federally subsidized stem cell research.

The Democratic National Committee also focused on health concerns in an ad released Monday, charging that Bush "stood with the big drug companies -- signing their Medicare law." The ad continues: "Blocking low-cost drugs from Canada. And under George Bush, prescription costs are up 22 percent. He's sided with the insurance industry as health premiums soared 57 percent."

Kurtz reported from Washington.

John F. Kerry, right, appears at a campaign event with actor Michael J. Fox, who has Parkinson's disease. The Democratic challenger promised to end limits set by President Bush on federally financed stem cell research.