California announced legal action tonight to suppress a "reprehensible" ballot initiative to outlaw homosexuality, on pain of execution.

The proposal, unlikely to advance, as it requires over 360,000 signatures to proceed, was submitted by lawyer Matthew McLaughlin to the California Attorney General's office late last month.

The "Sodomite Suppression Act" ballot proposes that gay people "be put to death by bullets to the head or by any other convenient method".

But Attorney General Kamala Harris said she was taking legal action to allow the state to effectively sideline the proposal.

"This proposal not only threatens public safety, it is patently unconstitutional, utterly reprehensible, and has no place in a civil society," she said in a statement.

"Today, I am filing an action for declaratory relief with the court seeking judicial authorisation for relief from the duty to prepare and issue the title and summary for the 'Sodomite Suppression Act.'"

She added: "If the court does not grant this relief, my office will be forced to issue a title and summary for a proposal that seeks to legalise discrimination and vigilantism."

The proposed initiative declares: "The abominable crime against nature known as buggery, called also sodomy, is a monstrous evil that Almighty God, giver of freedom and liberty, commands us to suppress on pain of our utter destruction even as he overthrew Sodom and Gomorrah.

"Seeing that it is better that offenders should die rather than that all of us should be killed by God's just wrath against us... the people of California wisely command, in the fear of God, that any person who willingly touches another person of the same gender for purposes of sexual gratification be put to death by bullets to the head or by any other convenient method," it reads.

California, like other US states, regularly holds elections on ballot initiatives - effectively referendums on proposed issues which must gather a minimum number of signatures to get on the ballot.