A LOT OF FORTUNE 500 COMPAnies are getting the jitters these days as Korean cargo ships unload automobiles, televisions, and other consumer goods at ports in California. But small companies, not the giants, may be most vulnerable to the new Korean competition.

The bloodiest battle will be fought in the $70-billion auto-parts suppliers' industry, where the vast majority of companies have fewer than 100 employees. The Big Three are intent on reducing their costs. "We're all scampering around the world. We need to find some way to squeeze $2,000 out of the cost of producing an automobile," explains Doug Nicoll, a Chrysler Corp. spokesman.

They may squeeze it out by jettisoning many small suppliers here in favor of the Koreans. U.S. makers of brakes, radiators, and other parts face a severe disadvantage: their labor costs are up to 13 times as high as are labor costs in Korea. "There's trouble ahead," says Dan Luria, a senior researcher at Industrial Technology Institute (ITI), in Ann Arbor, Mich. "The supplier base is going to get smaller." Korea exported $360 million worth of auto parts to the United States in 1984, up from $120 million in 1980. Last year,the total was expected to top $440 million, and it will go up as the Koreans get better at making cars. "Then they'll make quantum leaps into complex machined parts and subassemblies," says Luria.

Korean companies have won beach-heads in other areas populated by small and midsize companies. Northrop Corp., which farmed out some detail parts for its Boeing 747 upperdeck assemblies, recently contracted Daewoo Heavy Industries Ltd. to build that entire assembly. And Korean manufacturers of semiconductors and personal computers grabbed market share from small U.S. companies last year.

To compete with the Koreans on price, U.S. suppliers will have to invest in capital equipment. 'It's automate and get competitive, or get out," says David Morgan, director of computing technology at Motorola New Enterprises. "Just because they [the Big Three] did business with their daddies and granddaddies doesn't mean GM is going to buy from them anymore."