The cheaper dollar is making it easier for U.S. companies to export directly, but firms with a long-term interest in foreign markets will continue to invest in new plants overseas, the head of the Scottish Development Agency says.

Iain Robertson acknowledges that some U.S. companies have postponed foreign investments, but he points out that the decision to go international is long term.As companies become accustomed to doing business overseas, it's inevitable that they will make foreign investments in three to five years, he said in an interview while visiting New York last week.

I believe there's a lot of leverage that companies can get through integrated operations in these markets, he said. It's not just marketing, but also service and manufacturing.

Transportation costs are another factor that companies must consider. You're shipping a lot of air across the Atlantic along with your product, he said.

In addition, companies must be wary of currency swings that could knock them out of export markets they're just now entering, he said.

If the dollar swings back to $1.50 (against the British pound) in a few months, these companies are in big trouble, he said. The present exchange rate is about $1.75 to the pound.

Scotland has only 5 million people but has attracted some $3.5 billion in new foreign investments in the last four years. Most of the investment came

from U.S. companies attracted by the access it offers to the rest of the European Community, Mr. Robertson said.

Companies that have announced major new investments in the past 12 months include include Apollo Computer Inc., Chelmsford, Mass., and Maynard, Mass.- based Digital Equipment Corp.

Digital already employs some 1,300 people at a large mini-computer plant but is now investing in a new $125 million semiconductor plant in South Queens Ferry, a town near Edinburgh. Houston-based Compaq Computer Corp. is also planning a major new facility, and Avex Electronics Inc. of Huntsville, Ala., announced last September its plans to invest in a $10 million facility. Avex is a wholly owned subsidiary of the J.M. Huber Corp. of Edison, N.J.

We have to be as businesslike as the companies we're trying to attract, said the 42-year-old Mr. Robertson, who became the agency's chief executive last September. As a result, it refrains from using a scatter-gun approach and instead targets companies in specific industries - mainly electronics, health care and offshore oil exploration.

Scotland's success is demonstrated by the fact that four out of five U.S. companies with investments there have reinvested within five years, he said. You only reinvest if your expectations have been met.