The four misdemeanor charges accuse SoCalGas, a division of San Diego-based Sempra Energy, of failing to report the release of hazardous materials following the underground pipeline rupture and discharging air contaminants.

"While we recognize that neither the criminal charges nor the civil lawsuits will offer the residents of Los Angeles County a complete solution, it is important that Southern California Gas Co. be held responsible for its criminal actions," District Attorney Jackie Lacey said in a written statement.

Lacey's move came on the same day that California Attorney General Kamala Harris sued Southern California Gas Co, accusing the utility of violating state health and safety laws by failing to promptly control the escaping gas and report the leak to authorities.

The lawsuit also cites environmental damage caused by the uncontrolled release of 80,000 metric tons of methane, the prime component of natural gas and a far more potent greenhouse gas than carbon dioxide.

The leak stems from an underground pipeline rupture at the company's 3,600-acre (1,457-hectare) Aliso Canyon natural gas storage field. The largest such leak ever in California, at its height it accounted for a fourth of all methane emissions statewide.

The lawsuit amends a civil complaint brought in December by the Los Angeles city attorney and later joined by Los Angeles County. It seeks civil penalties and court orders requiring the utility to immediately take all steps necessary to mitigate the leak, repair the damage and prevent future discharges.

Several attempts to halt the methane release have failed, but the company said it hopes to plug the leak by the end of the month through a relief well.

The company said in a statement it would "respond to the lawsuit through the judicial process."

Last week, the South Coast Air Quality Management District filed a separate lawsuit against SoCal Gas seeking civil penalties of up to $250,000 a day for each of six pollution-related health and safety code violations.

The methane fumes have sickened scores of people and prompted the relocation of more than 6,600 households from the Porter Ranch community at the edge of the crippled underground gas storage field.

More than 20 private lawsuits have been filed on behalf of some of those residents.

(Reporting Steve Gorman and Dan Whitcomb in Los Angeles, Dan Levine in San Francisco and Brendan Pierson in New York; Editing by David Gregorio, Tom Brown and Bernard Orr)

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