LOS ANGELES — More than two years after the San Onofre nuclear power plant stopped production, California is looking to fill the gap left in its energy grid by the plant that provided enough electricity for 1.4 million homes.

On Thursday state regulators planned to make a major decision toward filling the hole left by San Onofre and its 2,000-megawatt capacity as they consider a proposal that would allow the plant’s co-owners — Southern California Edison and San Diego Gas & Electric — to find replacement power.

The plan calls primarily for the use of clean energy, but one environmental group says it could leave too much leeway for dirtier energy to leak in.

Under the proposal to the California Public Utilities Commission, the two utilities combined would be allowed to generate 1,500 megawatts of additional energy, so long as 60 percent of it came from sources like solar or wind, added efficiency, or voluntary conservation.

Evan Gillespie of the Sierra Club says that the plan “ups the odds that we’ll see even more polluting power plants in Southern California.”

The plan would require Edison to procure some 400 megawatts of electricity but would allow up to 700 megawatts via renewable resources or power storage. It would require SDG&E to procure at least 400 megawatts but would allow for up to 200 via cleaner power or conservation.

Production at the nuclear plant was stopped in January, 2012 when a small radiation leak led to the discovery of unusual damage to hundreds of new tubes that carry radioactive water. Last year operators chose to close it rather than fix the damaged equipment.

It was a key supplier to California’s electric grid, not just for its but for its strategic location between the state’s two largest cities, San Diego and Los Angeles.