SACRAMENTO — She has spent a fortune — $100 million and counting — and Republican Meg Whitman has not moved the dial against Jerry Brown in the gubernatorial race.

Despite an aggressive summer campaign in which she went on the offensive against Brown immediately after winning the GOP primary, Whitman remains stuck behind Brown, 37 percent to 34 percent, according to a survey released Wednesday night by the Public Policy Institute of California.

And her ramped-up attempt to appeal to Latino voters has not yet paid dividends: Brown’s lead over Whitman among Latinos is more than double — 42 percent to 18. Brown also holds a slight lead among independents, 30 to 28 percent. The poll surveyed 1,321 likely voters from July 6-20 with a margin of error of 2.7 percent.

In the same poll, U.S. Sen. Barbara Boxer held a 39 to 34 percent lead over Republican challenger Carly Fiorina.

The numbers show, political observers said, that Whitman’s strategy of using the typically slow summer months to attack Brown and cut into a core Democratic constituency may not be working, raising questions over whether Whitman might have to re-evaluate her overall approach.

“Coming so soon after the primary campaign, people might be tuning out,” said Jack Pitney, a government professor at Claremont McKenna College. “In the summer, people aren’t eager to pay attention to ads, and perhaps when they see another Meg Whitman ad, they virtually go someplace else. It may be that her message isn’t connecting.”

The Brown-Whitman matchups have remained fairly steady, though both have suffered erosion since January. Brown led 41 percent to 36 percent in January. Whitman overtook him in March, 44-39; and in May, Brown led 42-37.

Whitman, a billionaire ex-CEO of eBay, has spent $14 million since the primary on top of the $91 million she spent ousting GOP rival Steve Poizer.

Her television advertisements have attempted to tar Brown with the imagery of an entrenched, “failed” politician. While Brown has remained off the air, husbanding $23 million for the fall, a labor-backed independent group has spent about $6 million, airing ads in Southern California depicting Whitman as a liar.

“It shows you can spent a lot of money, but at the end of the day, if you’ve changed your positions on issues and told obvious lies, voters catch on to those things and they hold you accountable for them,” said Sterling Clifford, Brown’s spokesman.

“She’s been throwing everything against the wall and nothing seems to be sticking,” said Roger Salazar, spokesman for California Working Families 2010. “It says something about her, and about our own effort, but it also says Californians don’t seem to be interested in pressing the ‘Buy’ button on Meg.”

Whitman’s campaign declined to answer questions about campaign strategy, issuing only a statement.

“We know there will be many polls during this race,” Whitman spokeswoman Sarah Pompei said. “We’re confident that on Election Day in November, Californians will choose Meg’s leadership to create jobs, cut spending and improve education.”

Another poll, the Public Policy Polling survey, showed that 52 percent of voters — versus only 33 percent — believe there should be a legal limit on what a candidate can spend on his or her own campaign.

“California voters may be telling Meg Whitman that she can’t buy this election,” said Dean Debnam, president of Public Policy Polling, a Democratic firm based in Raleigh, N.C., that surveys races around the country. Public Policy Polling surveyed 614 likely California voters July 23-25 with a margin of error of 4 percent.

“It’s a hard slog for her,” Pitney said. “Who knows what her numbers would look like if she hadn’t spent all that money? Given the Democratic leanings of the state and Jerry’s name ID, a 3-point deficit isn’t bad. Nevertheless, I’m sure they’re disappointed and were hoping they’d be ahead at this point.”

In a state with a 13-point advantage for Democrats — 44.5 percent of registered voters are Democratic and 30.8 percent are Republican — Brown’s built-in advantage is carrying him so far, said Bill Whalen, a fellow at the Hoover Institution and former aide to ex-Gov. Pete Wilson.

“She’s staying even in what is a very hostile environment for any politician,” Whalen said. “The burden of proof is always for a Republican to prove they’re mainstream.”

Contact Steven Harmon at 916-441-2101.