LOS ANGELES - Environmentalists urged California regulators on Wednesday to reject a proposed expansion of the only offshore drilling operation still permitted in state waters along the Santa Barbara coastline, seizing on public outrage over last week’s nearby oil spill. Privately owned Venoco Inc is seeking permission to drill on 3,400 acres (1,400 hectares) of the sea floor within a state-designated coastal sanctuary adjacent to the company’s current offshore lease site. It said the plan would increase petroleum production by 6,400 barrels a day. That additional capacity, like the crude petroleum already being pumped from Venoco’s 50-year-old Platform Holly, would ultimately be added to oil supplies carried through the pipeline that burst on May 19 about 20 miles (32 km) west of Santa Barbara. The breach dumped as much as 2,400 barrels (101,000 gallons, or 382,000 liters) of crude onto a pristine stretch of shoreline and into the Pacific, leaving slicks that stretched over 9 miles (14 km) along the coast. Two state beaches were closed indefinitely, along with fishing in the area. The spill also prompted the California Lands Commission to postpone its first public hearing on Venoco’s offshore drilling proposal, originally slated for Tuesday, to June 24. On Wednesday, the conservation group Center for Biological Diversity sent a letter calling for the Lands Commission to deny Venoco’s application to drill on tracts of the sea floor placed off-limits to new energy development under a 1994 state law. Venoco’s proposal cites an exception under the statute that allows for adjustment of an existing offshore mineral lease to encompass oil reserves left out of its original boundaries. But opponents said the commission instead should order decommissioning of Platform Holly, which was built in 1965 and sends oil to shore through a subsea pipeline that is itself 45 years old. Petroleum from Venoco’s rig ultimately is added to refinery-bound supplies that get pumped through the failed 28-year-old transmission line owned by Texas-based Plains All American Pipeline. “It would be a grave mistake for the state to approve a project that will feed more crude into a pipeline system that just spewed thousands of gallons of oil into the Pacific,” said Miyoko Sakashita, the Center for Biological Diversity’s oceans program director. Venoco, which operates mostly in Southern California but is based in Denver, had no immediate comment.