ST. LOUIS — As baseball fans across Missouri watched the first game of the World Series, they saw Michael J. Fox, the actor-turned-activist for embryonic stem cell research, endorse Democrat Claire McCaskill for Senate and sharply criticize Sen. Jim Talent, the Republican incumbent who backed President Bush's veto of legislation to expand that research.

"They say all politics is local, but it's not always the case," said Fox, his body swaying uncontrollably because of Parkinson's disease. "What you do in Missouri matters to millions of Americans, Americans like me."

At the heart of McCaskill's campaign — and the campaigns of more than a dozen Democratic candidates running for the House, Senate and governor — is support for the controversial research and the possibility that it may unlock cures for a range of diseases and conditions affecting 100 million people nationwide.

Candidates from Maryland to Wisconsin and New Jersey to Illinois plan to spend the closing days of the election season emphasizing their support for the research.

Fox is scheduled to appear at a campaign rally Tuesday in Wheaton, Ill., to support Tammy Duckworth, the Democrat running to replace retiring Rep. Henry Hyde, R-Ill.

Candidates supporting embryonic stem cell research hope the issue will boost their prospects with a broad swath of voters more than it will hurt them with religious conservatives who believe that scientists are immorally destroying life in the pursuit of their goals.

"Yes, it has an impact on you when your priest talks about this issue, but I think it has a much bigger impact on you if your grandmother has Alzheimer's," said McCaskill, the Missouri state auditor.

Her eyes brimmed with tears as she talked about Fox's struggle with Parkinson's and about her high school boyfriend who died from ALS, a fatal neurological disease that attacks the nerve cells that control the muscles.

Along with the television commercial for McCaskill, Fox has done ads for Rep. Ben Cardin, running for the Senate from Maryland, and Wisconsin Gov. Jim Doyle, seeking re-election. Fox's efforts already have inspired a conservative backlash, with Rush Limbaugh suggesting Monday that the actor was "either off his medication or acting" when he showed symptoms of Parkinson's during the commercial.

Here in Missouri, a longtime bellwether for the national mood, the stem cell issue is particularly prominent because of a proposed constitutional amendment on the Nov. 7 ballot to prevent the research from being criminalized, as some legislators previously have tried to do.

The fight over the initiative has resulted in millions of dollars spent on commercials and billboards and lawn signs, as well as a massive grassroots effort involving churches throughout the state. Both sides complain that the other has lied to advance its cause.