George Soros, the multibillionaire investor, will donate $1 million to help pass Proposition 19, the marijuana legalization measure, which he endorsed Monday as "a major step forward."

The donation makes Soros, who is the chairman of a hedge fund and who founded the Open Society Foundations, the largest donor to the campaign after Richard Lee, an Oakland medical marijuana entrepreneur, who has spent at least $1.5 million on the measure.

It provides a huge lift to the Yes on 19 campaign, which had raised about $2.4 million by mid-October, as it launched cable television advertising Tuesday in the Los Angeles area.

Ethan Nadelmann, the executive director of the Drug Policy Alliance, one of the nation’s main advocates for reforming drug laws, confirmed the planned contribution on Tuesday.

"There’s no way to know what this means in terms of George Soros’ future commitments," he said, "but I for one hope that he will end up making the same commitment to broader marijuana law reform as he has since the mid-1990s to medical marijuana."

Soros has donated about $3 million to help pass three California initiatives, including the state’s 1996 measure to allow the use of marijuana for medical reasons.

Proposition 19, which would allow adults 21 and older to grow and possess marijuana, was Lee’s brainchild, and he has been the principal donor and spokesman for the cause. The wealthy donors who had bankrolled past efforts to change California’s drug laws were not involved in the campaign at the beginning and had largely stayed on the sidelines until the last few weeks.

Peter B. Lewis, a retired insurance company executive, recently donated $209,005, and George Zimmer, the founder and CEO of Men’s Wearhouse, donated $50,000. Zimmer had earlier donated $20,500. Both businessmen have supported past initiatives to soften the state’s drug laws, including the medical marijuana initiative.

Soros announced his support for the initiative, which would also allow cities and counties to authorize commercial cultivation and sales, in an opinion piece that was published online Monday evening by the Wall Street Journal. He called for marijuana to be regulated and taxed.

"Proposition 19 already is a winner no matter what happens on Election Day," he wrote. "The mere fact of its being on the ballot has elevated and legitimized public discourse about marijuana and marijuana policy in ways I could not have imagined a year ago."

-- John Hoeffel

Photo: Joshua Roberts / Bloomberg