In sharp contrast to foreign car companies that eagerly become international traders, U.S. manufacturers become skittish when urged to bring their business overseas, observers of the car parts industry say.

Gary D. Showalter, manager of the 1988 Eastern Automotive Aftermarket Show being held here, said many U.S. automotive parts manufacturers assemble pieces that could easily fit foreign cars.But they've avoided foreign marketing because of a fear of the unknown - customs clearances, differences in the laws, licensing agreements, he said.

Representatives of the many manufacturers attending the show acknowledged that exporting represents only a small part of their business.

A common excuse heard is: There's more than enough business here in this country, explained Paul Cunningham, a representative for Cloyes Gear & Products Inc. of Paris, Ark.

Some companies are interested in an overseas clientele. On Monday, the U.S. Department of Commerce sponsored an all-day workshop on exporting, attended by about 35 manufacturers, Mr. Showalter said. The push to encourage exporting is not being done so much to compete with imports, but simply to inform manufacturers that there is a larger market, he said.

Robert L. Schutte, director of international affairs for the Automotive Service Industry Association, said that if business is slow in the United States, and it hasn't been exactly booming in the past couple of years, then exporting offers a very good opportunity to increase sales and facility capability.

In addition, if you don't know how to sell your product in a foreign market, then it's much more difficult to compete with foreign companies selling in the United States, he said. Exporting gives you an outlook on how they compete here.

The small amount of exporting among U.S. automotive parts manufacturers is very peculiar, Mr. Schutte said. I suppose it's an about-face from the early days of the famous Yankee traders. This has become such a cushioned market . . . and they get so much business here that they don't have to go outside.

Large machinery, however, is a popular export item, Mr. Showalter said. For instance, Winona Van Norman of Winona, Minn., regularly ships large cylinder boring machines, crankshaft grinders and brake equipment to Puerto Rico, Jamaica, Africa and other countries, said sales representative Gerald Fogg.

It's hard to buy equipment like this overseas, he said. There may be only one or two places in all of South America that make machinery like this.

And Jack Cameron, a product line manager for Pioneer Barnes Group Inc. of Meridian, Miss., said that because his company offers a broader spectrum of engine and clutch components, we'll probably be going out and targeting overseas as a bigger market.

But some manufacturers assemble parts that are not in demand overseas, leaving out exporting as a viable outlet to increase business. George Dawson, a representative for the Keystone Cable Corp. of Philadelphia, said: They make lines and cables all over the world. In this business, the biggest thing is competition, and for overseas business it would be much more fierce than it is here.

At least one company, however, does not want to see exporting become popular. Melling Automotive Products of Jackson, Mich., proudly touts itself as a worldwide manufacturer, and sales manager Nick L. Behrendt said he does not want to see more companies wooing overseas customers.

By putting more people in the exporting business, the only way to get business is to discount the prices, he said. And with high overhead for exports, it is not feasible to cut prices, he said.

Some companies at the Big E show, which started Tuesday and ended Thursday, are familiar with both importing and exporting. The China National Auto Industry Import/Export Corp., which has a U.S. office in Detroit, does a brisk business in the United States selling Chinese auto parts.

Most of our business is obviously in China, said manager Xu Junqi, but we also sell in West Germany, Canada, here and other markets.