Southern California utilities, looking for ways to satisfy the region's demand for water, are exploring a plan to build a huge desalination plant in northern Mexico that would convert seawater into 100 million gallons of drinking water each day--enough to meet the daily needs of about 228,000 households.

Officials of the Metropolitan Water District, Los Angeles Department of Water and Power, Southern California Edison and the San Diego County Water Authority--agencies that supply virtually all water users in Southern California--said Thursday that they plan to move ahead on a $600,000, six-month study of the water recovery project.

"It's past the idea stage," said Gary Snyder, chief engineer for MWD. "The next phase is to find out who is going to buy the water and how to get it to whoever buys it."

As envisioned, the plant would be one of the world's largest desalting facilities and also would generate electricity.

Officials of the Bechtel Power Corp.--which will conduct the study--have told the utilities that a combination water and electric power plant similar to those used in Saudi Arabia can be built on the coast of Tijuana for $1.5 billion to $2 billion.

Tijuana, a border town next to San Diego, is being considered because of lower construction costs and fewer regulatory laws there, utility officials said. Mexico has fewer environmental and land-use regulations and there is no Mexican equivalent of the California Coastal Commission, which would have to approve a similar plant if it were built north of the border.

"We have talked with a lot of people in Mexico and they need water and they need power," said Leon Awerbuch, manager of power desalination for Bechtel, a San Francisco-based engineering firm that has designed and operated such plants worldwide.

Mexican officials could not be reached for comment on the proposal.

The study by utility companies apparently represents one of the more vigorous explorations in the region of desalination as a solution to tightening water supplies. Previous efforts to stretch available water supplies mainly have been limited to water conservation, reclamation of waste water for farming and, most recently, mandatory cuts.

In the past, the relatively low cost and steady supply of California water has by comparison made methods such as desalination too expensive. Currently, MWD sells an acre-foot of water--a standard measure equivalent to about 325,850 gallons, or roughly enough to supply two families for a year--for $230. Utility officials estimate that it would cost about $1,000 to produce a similar amount of water at a desalination plant.