LOS ANGELES (Reuters) - Regional air quality regulators in California voted on Saturday to require the utility responsible for a ruptured underground pipeline in the Los Angeles area to underwrite an independent study on the health effects of a huge methane leak from the site.

The natural gas leak in Aliso Canyon, just outside the Los Angeles neighborhood of Porter Ranch, began on Oct. 23 and ranks as the worst ever in California.

Odorized methane fumes sickened scores of people and led to the temporary relocation of thousands of residents from the northern Los Angeles community near the leaking storage field in Aliso Canyon.

The 4-1 vote on Saturday by a hearing board of the South Coast Air Quality Management District (AQMD), a regional agency, stopped short of requiring the utility to extract more gas from the crippled field than it already had pledged to siphon out, under orders from state officials.

Gas extraction is designed to ease pressure on the ruptured wellhead and slow the leak.

Lawyers from Southern California Gas Co, the owner of the facility, told the AQMD hearing board any requirement from them could not conflict with the orders from the state Public Utilities Commission and Governor Jerry Brown.

"We're going to comply with the law, we are going to do what they've asked us to do," Robert Wyman, a lawyer for SoCalGas, told the AQMD regulators at the meeting in Los Angeles.

After that, the board members required the utility to underwrite an independent study on the effects of the leak on local residents and imposed additional monitoring and reporting requirements on the utility.

"We may decide in the future to take additional steps but that's no reason not to take these steps now," said David Holtzman, one member of the board who voted for the order.

Los Angeles County health officials, who note that Porter Ranch residents have complained of such ailments as headaches and respiratory irrigation from an odorant in natural gas, have said past studies found only short-term health effects from the odorant. But they said continued health monitoring is needed.

Even so, disgruntled residents have demanded the 3,600-acre (1,457-hectare) facility, where surplus gas is pumped underground and stored until needed, be shut down altogether.

Many community members among the 300 attendees at the meeting at a Los Angeles hotel expressed displeasure at the limited scope of the AQMD's action. Some held up small signs that read "Shut it ALL down."

After Wyman, the SoCalGas attorney, addressed the AQMD hearing board, spectators sighed loudly and many of them left the meeting.

Tim O'Connor, director of California oil and gas for the nonprofit Environmental Defense Fund, said the AQMD was limited by an overlap of various government agencies.

SoCal Gas, a division of San Diego-based Sempra Energy, projects it may take until late February to plug the rupture through a relief well that engineers began drilling in December.

(Writing by Alex Dobuzinskis, additional reporting by Steve Gorman; Editing by Diane Craft)