LOS ANGELES, Dec 23 (Reuters) - Southern California Gas Co and the Los Angeles City Attorney reached an agreement on Wednesday on a plan for the utility to provide temporary housing for residents living near a massive underground natural gas leak, the Los Angeles Times reported.

The agreement requires the utility, one of the largest in the United States, to relocate residents in the northern Los Angeles community of Porter Ranch within 24 to 72 hours and to increase security for vacated homes, the newspaper reported.

Reuters could not independently confirm the report. Court documents could not be immediately obtained, and representatives for the City Attorney's Office could not be reached.

SoCal Gas said in a statement that it already had devised a relocation plan but agreed to a dispute-resolution process for dissatisfied residents. The company said it was already working with police to step up patrols around vacant homes.

The leak, detected on Oct. 23, is believed to have been caused by a broken injection-well pipe several hundred feet beneath the surface of the utility's 3,600-acre Aliso Canyon gas storage field.

The South Coast Air Quality District said it had received hundreds of complaints about the persistent rotten-egg smell of mercaptan, a chemical added to the normally odorless gas to help detect leaks. Many also have reported nausea, nose bleeds, headaches, breathing difficulties and other ill effects.

The Los Angeles Times reported that some 2,500 families were waiting to be relocated from the neighborhood and that SoCal Gas had paid for the relocation of 2,000 households as of Tuesday.

The utility insists that the leak, while a major public nuisance, poses no immediate public safety threat because the gas dissipates outdoors. But county health officials said long-term health effects from exposure to the gas are unknown.

SoCal Gas is owned by San Diego-based Sempra Energy. Its leaking storage field is the second-largest such facility in the Western United States by capacity, after a field in Montana.

The leak now accounts for roughly a quarter of the state's total emissions of methane, the principal component of natural gas and a far more potent greenhouse gas than carbon dioxide.

(Reporting by Curtis Skinner in San Francisco and Steve Gorman in Los Angeles; Writing by Curtis Skinner)