By Patrick McGreevy and Evan Halper, Los Angeles Times

SACRAMENTO — The number of Californians who can now vote has surged to record levels — passing 18 million for the first time — a leap that could affect the outcome of contests across the ballot next week.

More than 1.4 million new voters have signed up, nearly 50 percent of them online under a new law that kicked in six weeks ago allowing electronic registration. They tend to be younger and more left-leaning than the state’s general voting population, according to Political Data Inc., a bipartisan firm that analyzed county reports.

That gives Democrats, who already dominate state politics, a big boost; they outnumber Republicans among the new voters by more than 2 to 1. The highest number of registered voters until now was 17.3 million, in February 2009.

The newly enfranchised could loom large in Gov. Jerry Brown’s push for tax increases, which is teetering in the polls. Brown has been pitching Proposition 30 to college students lately in a blitz of campaign appearances and social media outreach efforts expected to last until election day.

Independent voters, whose numbers also have risen, are considered key to Brown’s effort. A third of those who recently registered did so without a party preference or with a minor party.

The fresh registrants also could tip the balance in congressional races where Democrats hope to make gains in their uphill battle to retake control of the House; in more than a dozen House districts, Democratic registration rose slightly. And the new voters could help Democrats seeking to secure the state Senate and Assembly supermajorities required to raise taxes.

Online registration is the California Legislature’s answer to “voter identification” laws being promoted elsewhere with requirements that residents produce driver’s licenses or other identification before being allowed to vote. Civil-rights activists say such rules are intended to intimidate citizens and drive down election participation by the poor.

“While other states created illegitimate ways to suppress the vote, we found ways to increase the voter rolls,” said state Sen. Leland Yee, D-San Francisco, who wrote the online voter registration law. He called the program “a tremendous boost to young people and first-time voters.”

Gov. Jerry Brown signed the law last year over the objections of some GOP lawmakers, who expressed concern that electronic registration would invite fraud.

According to Political Data, a sizable share of the surge happened late. About 15 percent of the online registrants filled in their forms on the Internet on Oct. 22 — the deadline for next week’s election — amid various groups’ get-out-the-vote drives that day on Facebook and Twitter.

The numbers will rise further as some counties finish their tallies this week, said Paul Mitchell, vice president of Political Data. He predicted the final number will be about 18.4 million registered California voters when the secretary of state releases official statistics Friday.

Mitchell said online registration “created an avenue for a lot of people to register who would not have gone to the DMV and picked up a form or had someone harass them to register at Target.”

Other factors, such as a growing pool of voting-age Californians and the registration increase that typically accompanies a presidential election, were also at work, said Kim Alexander, who heads the nonpartisan California Voter Foundation. Her group promoted the new law.

She said the online effort brought in “typically underrepresented” young residents.

In some areas, registration increased by as much as 10%. That shifts the dynamic in at least two state legislative races.

In the 40th Assembly District in San Bernardino County, Democrats have reversed a GOP registration edge. Republican incumbent Mike Morrell of Rancho Cucamonga is fighting Democrat Russ Warner, also of Rancho Cucamonga, for the newly drawn seat.

And Democrats regained an advantage they had previously lost in a hotly contested race for the 31st state Senate District, in Riverside County. Republican Assemblyman Jeff Miller of Corona is running there against Democrat Richard Roth of Riverside.

Meanwhile, GOP officials had anticipated the Democratic uptick and were working to blunt its effect by scrambling to register more Republicans. They say some new GOP voters are not reflected in the Political Data report.

“We will figure out whether it makes a material difference on election day,” said Bob Huff (R-Diamond Bar), minority leader in the state Senate.

Republicans expressed doubt that the online system had effectively rooted out people not eligible to vote.

“There are not enough safeguards to prove that someone’s online identity matches their true identity,” said Assembly Republican leader Connie Conway of Tulare.

Where Republicans see safeguards, Democrats see barriers. Brown this year signed a law, also over GOP opposition, that a few years from now will allow Californians to register to vote on election day.