Backers of Proposition 19, which would have legalized recreational marijuana sales and use in California, said Wednesday that they would try to return to the ballot in 2012 with another attempt to pass the measure.

Although Prop. 19 lost handily Tuesday, the fact that millions of Californians supported it means marijuana advocates have a solid base of support, proponents said.

"It's clear that the electorate has spoken," Dale Jones, a spokeswoman for Prop. 19, said at a news conference in Oakland. "We have proven that the skull-cracking criminalization has failed, and we won't tolerate it any more. So we've already moved this conversation forward."

The measure, the nation's most sweeping proposal ever to legalize marijuana sales and use, would have legalized possession of as much as an ounce of marijuana for personal, recreational use by anybody 21 or older, and would have allowed people to grow cannabis in a 5-by-5-foot space.

It also would have permitted local governments to regulate and tax commercial sale and production, which proponents said would have injected billions of dollars to help shore up budgets.

Richard Lee, founder of the Oaksterdam cannabis university in Oakland and the author of Prop. 19, noted that the effort "got more votes than Meg Whitman."

"It's just the beginning," Lee said. "We knew this was just one battle in a big war."

Opponents of the measure argued that its provision that local governments set their own regulations and taxes would set up a confusing snarl of rules that varied city to city, county to county - and would still be illegal under federal law.

That message was reinforced last month when U.S. Attorney General Eric Holder said he would "vigorously enforce" federal anti-pot laws when it came to recreational use, no matter what Californians decided.

On Wednesday, Jones called Holder's announcement an "October surprise" that may have contributed to Prop. 19's defeat.

Roger Salazar, spokesman for Public Safety First, the principal organization opposing the measure, has said voters rejected the measure because the risks of legalizing the drug were "too scary."