JEFFERSON CITY, Mo. — The battle over stem-cell research in Missouri doesn’t lack for star power.

Ailing actor Michael J. Fox, rock star cancer-survivor Sheryl Crow, Super Bowl hero Kurt Warner, World Series pitcher Jeff Suppan, and celebrities galore have all given voters their two cents.

Their fame threatens to overshadow the tight Senate race between Senator Talent, a Republican, and his Democratic challenger, Claire McCaskill.

As the November 7 elections near, Missouri’s Senate race is intertwining with a ballot measure that would engrave the right to conduct embryonic stem cell research into the state constitution. Ms. McCaskill supports it; Mr. Talent opposes it.

The ballot initiative and Senate contest already have cost around $30 million each, counting money raised or spent by various campaign committees, the candidates and their political parities.

Ms. McCaskill’s campaign began airing ads over the weekend featuring Mr. Fox, who while shaking from the effects of Parkinson’s disease, urges voters to elect Ms. McCaskill because of her support for stem cell research. The ad prompted criticism from conservative commentator Rush Limbaugh.

The coalition supporting the initiative — which recent polls show has the support of 58% of likely voters — also has run ads featuring Ms. Crow, a native Missourian.

The ads prompted a group opposing the ballot initiative to hasten its own ad. That spot features five celebrities — including Mr. Warner, who led the St. Louis Rams to the 2000 NFL title; “Everybody Loves Raymond” actress Patricia Heaton, and Mr. Suppan.

The ad also features actor James Caviezel, who portrayed Jesus in “The Passion of the Christ,” and Kansas City Royals baseball player Mike Sweeney, who is deeply religious.

With all the attention, the stem cell initiative could help determine the outcome of Missouri’s Senate race — and thus control of the U.S. Senate. Democrats need to gain six seats nationally to wrest control of the chamber away from Republicans, and recent polls show Mr. Talent and Ms. McCaskill about even.

“Clearly, Claire McCaskill thinks that it would be advantageous for her to be linked to it,” political scientist Dave Robertson of the University of Missouri-St. Louis said. “Whether or not that’s borne out, it’s really going to be hard to tell.”

Missourians have a recent history of being drawn to the polls by high- profile ballot issues. An August 2004 constitutional amendment banning gay marriage attracted more votes than any other contest on the ballot.

Opponents of the stem cell initiative are hoping a similar religious-based movement can spur them to victory this year. Their attention is focused on ballot language that, while banning the cloning of human beings, allows an embryonic cloning technique that opponents contend destroys early human life.

That opposition is the main reason why anti-abortion voter James Cochran Jr., 43, says he will be casting his ballot for Mr. Talent. He recently was driving his parents’ van plastered with six “pro-life” bumper stickers, including one declaring “Vote No on Amendment 2. Defeat the phony cloning ban.”

Less flamboyant but equally passionate is Sharon Fockler, 63, who declares: “I’m for the stem cells, and I’m going with McCaskill.” Ms. Fockler explains that she’s voting for the Democrat primarily because she’s dissatisfied with Republicans in Washington, not specifically because of her support for stem-cell research. But the correlation still exists.

Whether the correlation will carry on Election Day is the big unknown. “There’s no question that the stem cell, and a few of the other ballot measures that are out there, are going to be energizing the different voting groups,” the chairman of the political-science department at Westminster College in Fulton, Kurt Jefferson, said.

But Messrs. Jefferson and Robertson both are leery of directly linking the stem cell initiative and Senate race, especially considering that polls show the war in Iraq to be a prime issue Senate voters.

There has not necessarily been a correlation between successful Missouri ballot measures and candidates. Republican John Ashcroft, a staunch gambling opponent, easily won Missouri’s 1994 Senate race even as voters approved an expansion of state-sanctioned gambling by allowing slot machines on riverboat casinos.

“Missourians are notorious for voting one direction with a ballot measure but maybe sending another message with the member going to Congress,” Mr. Jefferson said.