LOS ANGELES (AP) _ Chevron USA is trying to find the source of potentially explosive petroleum fumes along the beach in suburban Manhattan Beach, less than two miles from the oil company's refinery.

The company already is spending $700,000 to drill 42 test wells near the refinery to find the extent of leaks that may be responsible for a gasoline slick on the underground water table and persistent fumes throughout the area.

Norman LeRoy, environmental affairs manager for the refinery in El Segundo, said Chevron would conduct further tests to determine the source of the Manhattan Beach vapors. The answer could come by Monday, he said Wednesday.

''We know there are hydrocarbon vapors along four blocks of the beach,'' LeRoy said. ''But the sources of those vapors are still very much in doubt.''

He suggested the fumes might have leaked from sewer lines in the area or from a nearby service station.

Aside from pollution concerns, LeRoy said gasoline vapors are explosive in a confined space, such as a basement or garage.

Chevron's announcement came less than two weeks after the oil company revealed its plans to deal with the problems in El Segundo.

Officials said gasoline leaking from the 75-year-old refinery - possibly decades ago - had formed a slick on the water table about 70 feet underground.

The problem was detected after city crews smelled gasoline vapors while excavating for a construction project.

''In a nutshell, there seems to be a strong possibility that the gasoline vapors in the ground are coming from the (gaoline) pool (underground),' ' LeRoy said.

The company later began tests to determine if petroleum fumes could be found underground anywhere else in the vicinity, which led to the Manhattan Beach discovery. Those tests are continuing, LeRoy said.