LOS ANGELES (AP) _ Most of the oil spilled when a ship's anchor ruptured a pipeline in Santa Monica Bay will evaporate or be cleaned up, but it still could have lasting effects on the ocean food chain, officials said.

''I consider this a very significant spill,'' said Madelyn Glickfeld, a member of the California Coastal Commission. ''Just because the stuff is less visible than crude oil doesn't mean it's not environmentally damaging.''

About 300 workers, wearing hard hats and yellow rain slickers and gripping absorbent pads, took to the beaches of Malibu on Monday to mop up the light lubricant as it came ashore.

About 20,000 gallons of the ''gas oil,'' a mixture of diesel and naphthalene, escaped from an underground pipeline Saturday night when the OMI tanker Dynachem's anchor tore a hole in a hose leading to the pipeline.

The U.S. Coast Guard characterized damage to the beaches as slight, but acknowledged the spilled oil mixture was likely to linger in the ocean food chain - the chain of organisms from smallest to largest, with the larger ones eating the smaller ones.

''This is a fairly toxic kind of material, more toxic than crude oil,'' said Tim Rowe, a Coast Guard spokesman.

Rowe said the mixture didn't directly threaten fish but would affect single-cell organisms such as brine shrimp and various kinds of larvae.

''This is the very important start of the food chain for other animals, including whales. It does create more damage in the long run,'' he said.

The spill killed 10 birds, most of them Western grebes. Eight other birds, including two loons, were found oil-soaked but living.

Malibu residents on Monday complained that the pungent odor from the spill was giving them headaches and nausea, said City Councilman-elect Larry Wan. The area northwest of Los Angeles is home to many celebrities.

Surfrider State Beach, a mile-long surfing area and backdrop for countless beach movies, was closed.

The incident was the second spill from a Southern California offshore mooring facility in about a year and immediately prompted questions about oil tanker and pipeline safety.

Environmentalists recalled the much more damaging 400,000-gallon Huntington Beach spill in February 1990, caused by an anchor puncturing a tanker. They demanded a moratorium on offshore loading and unloading.

''This is the most basic kind of negligence: the dropping of an anchor on a pipeline,'' Bob Sulnick, executive director of American Oceans Campaign. ''We have the technology to put people on the moon and have Patriot missiles shoot down Scud missiles. We could certainly know where to drop our anchors.''