JEFFERSON CITY, Mo. (AP) -- Triple-digit temperatures appeared to be keeping some St. Louis voters from voting in Tuesday's primaries, but heated feelings about the federal health care overhaul seemed to be driving higher-than-expected turnout elsewhere in the state.

Missourians were selecting Democratic and Republican candidates for several offices, including U.S. Senate, where Democratic Secretary of State Robin Carnahan and Republican Congressman Roy Blunt are headlining the ballot.

But an assistant Greene County clerk said Proposition C -- an attempt to defy a new federal requirement that most people have health insurance -- seemed to be driving turnout higher than the projected 25-30 percent in the Springfield area.

In St. Louis, Board of Election Commissioners deputy director Gary Stoff said hot weather appeared to be a factor in light turnout. Temperatures exceeded 100 degrees in much of the state on Tuesday.

"Things are going very slowly," Stoff said. "I guess the combination of an off-year primary and the heat, which is pretty oppressive, is helping to keep down the number of voters so far."

City election officials had projected turnout in the range of 15-20 percent. "I think we'll hit the 15 percent," Stoff said. "I'm not sure about the 20."

Many supporters of Proposition C said they took exception to the government forcing mandatory health care upon them.

"I believe that the general public has been duped about the benefits of the health care proposal," said Mike Sampson of Jefferson City, an independent emergency management contractor who would only say he was in his 60s. "My guess is federal law will in fact supersede state law, but we need to send a message to the folks in Washington, D.C., that people in the hinterlands are not happy."

Don Mayse, 52, a suburban St. Louis firefighter, agreed.

"I just believe people have the right to choose their own health care, whether they want it or not. I don't think the government should tell you what to pay for."

Kathy Ward, a 57-year-old Columbia nurse, said she voted against the health care ballot measure.

"The fact remains, people have the right to have health care, and they should get it," she said. "It helps make for a healthier society."

Tommie Pierson, a 64-year-old pastor from north St. Louis County, called Proposition C "an effort to usurp the Obama health care plan. That's wrong, I believe. We should be backing the president."

In the Senate race, Michiko Smith, a 36-year-old administrator for Nike, said he backs Carnahan.

"I'm sticking with the Democratic program and I'm sticking with what she stands for, and what the Carnahan family has stood for over the years," he said.

Carnahan is the daughter of former Missouri Gov. Mel Carnahan. Blunt is the father of former Missouri Gov. Matt Blunt.

"I'm very conservative and a Republican," said retired Florscheim Shoes worker Ralph Higgins, 58, of Jefferson City, who said he voted for Blunt in part because of his support for gun owners' rights. "I've liked what he's done in the past -- his voting record."

A November general election contest between Blunt and Carnahan would mark the first time two political dynasties have faced off directly.

Members of the two families have served at almost every level of government, yet both Blunt and Carnahan have played up some humble attributes.

Blunt, 60, recalls how he was raised on a dairy farm in southwest Missouri in a home that lacked running water and insulation. Carnahan, who turns 49 on Wednesday, stresses that although she lives in St. Louis, she still helps run her family's cattle farm in Rolla.

Carnahan is in her second term as secretary of state. She is running for Senate on the 10-year anniversary of the death of her father and one of her brothers. They died in an October 2000 plane crash while Mel Carnahan was campaigning for the Senate.

Blunt is in his 14th year in the U.S. House. He previously served as secretary of state in the 1980s and early 1990s.

Missouri's ballot also featured several competitive Republican primaries for Congress -- including one for the seat being vacated by Blunt and another for the nomination to challenge longtime Democratic Rep. Ike Skelton.