SAN FRANCISCO — A proposition that a prosperous farmer brought to the California ballot would threaten two ambitious water and rail projects that Gov. Jerry Brown is pushing, requiring voters’ OK before launching any state building project requiring $2 billion or more in revenue bonds.

Proposition 53, if voters approve it on Nov. 8, could force Brown’s administration to hold statewide votes on funding for two controversial mega-projects that he is trying to get well underway before he leaves office in 2018.

Those are a $68 billion Los Angeles-to-San Francisco bullet train, and a $15.7 billion plan to build two giant tunnels to carry water from Northern California’s largest river south, mainly for use by Central and Southern California farms and cities.

While Brown has not spoken publicly on farmer and canner Dino Cortopassi’s measure, the governor has made defeating it one of his priorities for the November election, according to a fundraising letter that the state Democratic Party sent lobbyists and others in his name in August.

California is known for ballot initiatives compelling public votes on financing issues that make populists applaud and government budget-makers cringe, as with the landmark Proposition 13 in the 1970s. That measure limited increases in property taxes.

When it comes to securing up-front money for big building projects, like bridges, dams or prisons, California already requires a public vote on general-obligation bonds, which are repaid by the taxes that Californians pay.

Proposition 53 would add the statewide-vote mandate to projects financed by more than $2 billion in revenue bonds, which use revenue from tolls or other user fees to repay.

California’s bipartisan Legislative Analyst’s Office, in its review of Proposition 53, calls it “unlikely there would be very many projects large enough to be affected” if the measure passes.

The tunnels and high-speed rail projects likely would be, the analysis says, and “it is possible other large projects could be affected in the future, such as new bridges, dams, or highway toll roads.”

While the tunnels may be the main project at stake, both sides on the revenue-bond measure insist their stand isn’t primarily about the tunnels.

Cortopassi is a former Republican and a former contributor to the conservative Koch brothers who has since become a Democrat. With his family he funded the more-than-$4.5 million petition-circulating campaign that brought the revenue-bond measure to the ballot.

The proud child of Italian immigrants who made his fortune partly by canning Central Valley tomatoes, Cortopassi opposes the tunnels, but says his ballot measure is about stopping the state from launching into giant projects, with murky financing, at will, through revenue bonds.

“I call it cockroach debt,” Cortopassi said. Cockroaches and revenue bonds, he said, “are born and expand in the dark. You want to get rid of cockroaches? Turn on the light.”

Opponents of Cortopassi’s measure contend it could force purely local projects to seek statewide voter approval, which Cortopassi’s camp denies. Opponents also argue the measure could limit urgent rebuilding after an earthquake or other disaster.

“It’s one of the most complex and unsexy initiatives on the ballot but it’s probably one of the most important,” said Steven Maviglio, a spokesman for the campaign to defeat Proposition 53.

Maviglio calls the measure unworkable. “The main thing is it will hold up a lot of (local) infrastructure projects by letting other cities vote on it.”

Speaking of Cortopassi, Maviglio said, “if he had wanted to kill the tunnels he should have written something that would kill the tunnels, instead of a hundred other projects.”

The state Democratic Party, the state Chamber of Commerce, the California State Building and Construction Trades Council, and scores of local chambers, construction and other industry associations, unions and other groups have come out against Proposition 53.