UPDATE 1-BP starts L.A. refinery gasoline unit work -sources

(Adds details, background)

HOUSTON, Jan 10 (Reuters) - BP Plc (BP.L) was beginning a massive overhaul on Thursday of the gasoline-producing unit at its Los Angeles-area refinery, according to sources familiar with refinery operations.

Up to 4,000 contract workers are expected to be employed in the two-month overhaul of the 103,000-barrel-per-day (bpd) gasoline-producing fluidic catalytic cracking (FCC) unit at the 265,000 bpd refinery in Carson, California, the sources said.

A BP representative declined to discuss operations at the Carson refinery.

A related alkylation unit will also be worked on while the cat cracker is shut, the sources said.

The FCC work is expected to be in full swing no later than Saturday.

Los Angeles-area wholesale gasoline prices were unaffected by the cat cracker's shutdown as BP has laid in supplies of gasoline and intermediate feedstocks to carry it through the overhaul.

Los Angeles wholesale market gasoline prices fell 10 cents on Thursday on perception of full supplies in the region.

The U.S. Energy Information Administration reported on Wednesday that West Coast gasoline inventories rose 1.6 million barrels last week to 33.6 million barrels. (Reporting by Erwin Seba; Editing by Christian Wiessner)