The Giuliani campaign insisted that it had nothing to do with the ballot initiative; the Clinton campaign also said it had no involvement, beyond opposing it. The same cannot be said for loyalists of the two camps.

The lion’s share of the work and money has come from supporters of Mr. Giuliani and Mrs. Clinton.

One of Mr. Giuliani’s top fund-raisers, Paul Singer, a New York City hedge fund executive, donated nearly all the money raised so far in support of the measure — roughly $170,000 — to be used to help gather signatures to qualify it for a statewide vote. Organizers have until Nov. 29 to collect the signatures of more than 400,000 registered voters for the initiative to appear on the ballot next June.

The money for the measure was donated through Take Initiative America, an organization led by a lawyer in Missouri who has also donated to Mr. Giuliani’s campaign. A spokesman for the Missouri group, Jonathan Wilcox, was once a spokesman and speechwriter for Bill Simon, a one-time Republican candidate for governor of California and now co-chairman of Mr. Giuliani’s California campaign.

The effort to topple the measure has been led by Chris Lehane, who first raised the alarm bells when a draft of the initiative began circulating in July and then encouraged Howard Dean, the Democratic Party chairman, and other national Democrats to oppose it loudly.

Mr. Lehane, who worked on Bill Clinton’s first presidential campaign and was a special assistant counsel in his administration, enlisted various elected officials who support Mrs. Clinton, including the Democratic mayors of Los Angeles, San Francisco and Oakland, and the Democratic leaders of the State Legislature. Steve Bing, a Hollywood producer who has raised over $100,000 for Mrs. Clinton, has also lent his name to the effort.

The bulk of the $200,000 in costs for the Democratic side, including television advertisements denouncing the proposal, were paid for by Thomas F. Steyer, a California hedge fund executive who has raised at least $100,000 for Mrs. Clinton’s presidential campaign. The money for the effort against the ballot measure was donated to a committee, Californians for Fair Election Reform, created by Mr. Lehane and Mr. Steyer.

“Thank God they did it, and thank God for our activists,” said Art Torres, chairman of the California Democratic Party. “I can’t think of any single threat more dangerous.”