After enduring months of expensive campaigning by corporations and candidates, California voters go to the polls today to decide primaries for governor and U.S. Senate and races for a number of statewide and local offices - as well as ballot measures to allow the San Francisco 49ers to build a new stadium in Santa Clara and to change primary elections in the state.

Just one-third of California's almost 17 million registered voters - a record-low turnout - are expected to weigh in, according to an analysis by the Field Poll.

The lack of voter interest reflects the lack of drama in two high-profile Democratic races, where Attorney General Jerry Brown, a candidate for governor, and incumbent Sen. Barbara Boxer face no strong competition from their party.

By contrast, GOP voters will decide two of the most-watched political contests in the nation - and whether to nominate women for the first time as Republican candidates for governor and U.S. Senate.

In California's gold-plated GOP governor's race, first-time candidate Meg Whitman - the former eBay CEO who has put $71 million of her own money into the race - leads state Insurance Commissioner Steve Poizner, who has dropped $24 million of his money.

Democrat Brown, the former two-term governor and Oakland mayor, cleared the field of any serious contenders months ago.

Seeking challenger to Boxer

In the GOP U.S. Senate race, former Hewlett-Packard CEO Carly Fiorina - who has invested more than $5 million of her own funds in her campaign - is leading in the polls against moderate former South Bay Rep. Tom Campbell and Assemblyman Chuck DeVore of Irvine, a Tea Party favorite.

The winner will challenge Boxer, who has faced a feisty but longshot challenge from former Slate.com blogger Mickey Kaus as she seeks a fourth term.

California voters also will decide who will square off in November for the lieutenant governor's post. On the Democratic side, San Francisco Mayor Gavin Newsom, with the edge in fundraising, polling and endorsements, is the favorite over Los Angeles City Councilwoman Janice Hahn, who has attacked him for not knowing what the position entailed several months before announcing he was running.

In the GOP primary, recently seated Lt. Gov. Abel Maldonado, a moderate from Santa Barbara County, is facing a challenge on the right from Sen. Sam Aanestad of Grass Valley (Nevada County).

Two district attorneys from opposite ends of the state appear to be the favorites to win their party's nominations for attorney general in crowded fields. San Francisco District Attorney Kamala Harris, a Democrat, has polled well against six challengers but has been hit hard over the city's drug-lab scandal by her most well-funded opponent, former Facebook privacy officer Chris Kelly, who has put $12 million of his own money into the race.

GOP attorney general's race

At the same time, Republican Los Angeles District Attorney Steve Cooley has been attacked by his right-of-center opponents, state Sen. Tom Harman and former Chapman Law School Dean John Eastman, for his criticism of the state's "three strikes" sentencing law.

California voters also will decide two measures that would affect elections and campaigns.

Proposition 14 would place all candidates from all parties in the same primary, with the two candidates with the most votes advancing to the general election even if they're both from the same party. Proposition 15 would create a pilot program to publicly fund the campaigns for secretary of state.

Two ballot measures with major financial backing from corporations also will be decided.

The campaign for Proposition 16, supported by $46 million in funding from Pacific Gas and Electric Co., would bar communities, including San Francisco and Marin County, from forming public power agencies without the approval of two-thirds of local voters.

At the same time, the campaign for Proposition 17 - which would offer discounts to drivers who have maintained continuous coverage while allowing insurers to raise rates for drivers whose coverage has lapsed, has received $17 million from its chief backer, Mercury Insurance.

Santa Clara votes on 49ers

Perhaps the highest-profile measure in the Bay Area is Santa Clara's Measure J, which would clear the way for the San Francisco 49ers to build a new $937 million stadium next to the Great America amusement park.

The team, which has spent more than $4 million on the campaign, promises that no money from the city's general fund would be spent on the stadium. Opponents, who have raised about $20,000, argue that the stadium deal is too big a risk for Santa Clara.

Bay Area voters also will decide a dozen tax measures to benefit local school districts.

Chronicle staff writers John Wildermuth, John Coté, Nanette Asimov, Marisa Lagos and Carolyn Jones contributed to this report.