Democratic presidential hopeful Hillary Clinton has stopped her slide in California and holds virtually the same double-digit lead she had over Vermont Sen. Bernie Sanders three months ago, a new Field Poll has found.

Clinton, the former first lady, New York senator and secretary of state, has the support of 46 percent of the likely voters in June’s Democratic presidential primary, down a single point from November.

Sanders, a longtime independent who has rallied liberals and progressives to his cause, remained at 35 percent, the same as his October showing. But that’s a huge improvement from February, when the poll found him trailing Clinton, 73 to 10 percent.

But Clinton’s continuing popularity in California will make it tough for Sanders to move past her to victory, said Mark DiCamillo, the Field Poll’s director.

“Everything depends on events,” he said. “Sanders needs to hit an inside straight. If he wins Iowa and New Hampshire, things could change.”

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Sanders’ dilemma

Sanders’ California numbers show why it will be hard for him to maintain any momentum he might gather from strong showings in those early states. While current polls give Sanders, a self-described Democratic socialist, a lead in New Hampshire and put him within striking distance in Iowa, those two overwhelmingly white, rural states have little in common with the Democratic Party’s urban and ethnic base.

In California, for example, Sanders and Clinton are tied among white, non-Hispanic voters, but the front-runner has an overwhelming 57 to 32 percent lead among the state’s growing legion of ethnic voters.

That solid ethnic support is likely to buttress Clinton’s efforts when the contests move to South Carolina on Feb. 27, and the so-called SEC primary in the South on March 1, named after the Southeastern Conference in college athletics.

“Whether Sanders is successful depends on him building momentum and taking away the air of inevitability from the Clinton campaign,” DiCamillo said.

But while momentum is important in politics, it’s not the only concern, DiCamillo added.

“There was a lot of momentum in (Barack) Obama’s direction in 2008 coming to California’s primary, but Clinton still hung on to win,” he said.

Female voters crucial

Clinton’s overwhelming support from female voters was key in 2008 and probably will be again this June. Of those women likely to vote in the primary, 49 percent support Clinton, versus 32 percent for Sanders. And in California, women make up 58 percent of all registered Democrats.

Sanders gets his support from the youngest and most liberal voters, with at least a sprinkling of help from the “anyone-but-Clinton” crowd.

Among likely voters ages 18-39, Sanders thrashes Clinton, 57 to 32 percent. But Clinton has a better than 30-percentage-point lead among all older voters. And while Sanders outpolls Clinton 47 to 45 percent with liberal Democrats, she’s the choice of 46 percent of all voters who don’t identify themselves as liberals, compared with 25 percent for Sanders.

Sanders also gets a boost from the Democrats’ primary rules, which, unlike those of the Republicans, allow voters with no party preference to cast ballots. Those non-Democrat primary voters back Sanders by a 50 to 30 percent margin.

In a closed primary, with only Democrats voting, “Clinton would have a 19-percentage-point lead instead of 11 percentage points,” DiCamillo said.

A Gallup Poll released last month found that Clinton was the nation’s most admired woman for the 20th time, but those years in the public spotlight have come with a cost. While almost all California voters, Democrats and Republicans, have an opinion on Clinton, it often isn’t a favorable one.

Candidates’ popularity

Among all registered California voters, 50 percent have a favorable impression of Clinton and 44 percent don’t much like her. That compares to a 52 to 31 percent split for Sanders.

Of voters who describe themselves as strongly conservative, 84 percent have an unfavorable view of Clinton, while 69 percent disapprove of Sanders, even though by any measure Sanders is far more liberal than Clinton or any other major-party candidate in recent years.

“Clinton is a lightning rod, especially for Republicans,” DiCamillo said. “There’s a continual negative drag on Clinton.”

That even shows up among likely voters in the June primary. While 71 percent of those who support Clinton have a favorable impression of Sanders, only 54 percent of the Vermont senator’s backers say the same about Clinton.

The poll is based on a telephone survey taken between Dec. 16 and Jan. 3 of 1,003 registered voters, including 329 likely to vote in June’s Democratic presidential primary. The margin of error is plus or minus 3.2 percentage points for the entire sample and plus or minus 5.6 percentage points for the Democratic primary sample.

John Wildermuth is a San Francisco Chronicle staff writer. E-mail: jwildermuth@sfchronicle.com Twitter: @jfwildermuth