Fokker, the Dutch aerospace company, announced formation last week of a new U.S. subsidiary in a major step designed to strengthen its position in the United States.

The move is an indication of the great potential that foreign aircraft manufacturers see for sales to the larger commuter airlines, the fast-growing segment of the airline industry whose opportunities have been so enhanced by the Airline Deregulation Act.

Fokker produces two airplanes that it thinks will appeal increasingly to the commuter airlines operating relatively short-distance flight. But they also would operate well on the somewhat longer flights that the larger airlines are dropping on grounds that they're too short to be served economically by larger jets. Those planes are the Fokker F27 Friendship, a twin project seating between 40 and 56 passengers, and the Fokker F28 Fellowship, a twin fanjet seating between 80 to 85 passengers.

Fokker has maintaned a North American Marketing Division in the United States for several years and has already made some sales; one U.S. commuter currently operates the F27, two more are about to, and two more airlines are about to begin services with the larger F28.

But Fokker said the dramatic increase in commuter airline service that already has come about as a result of deregulation and the future growth it expects has led it to strengthen its U.S. activities.

Based in Washington, the new Fokker Aircraft U.S.A. Inc., a wholly owned subsidiary of Fokker B.V. in the Netherlands, has full financial and contractual powers for the marketing, sales and support of Fokker's commercial aircraft products. It also will be responsible for implementing and maintaining the U.S. spare parts stock and distribution center for Fokker's American customers. Fokker recently signed a contract with E-systems Inc. of Dallas to operate the center for it.

Right now, one U.S. commuter operates the F27 propjet, although two others are preparing to. Swift Aire Lines of San Luis Obispo, Calif. currently operates a fleet of three. Pilgrim Airlines, based on New London, Conn., has taken delivery of an F27 and experts to begin using it soon. Also, Mississippi Valley Airlines of LaCrosse, Wis., gets the first of four F27s it has ordered in September.

First deliveries of Fokker's F28 fanjet have been made to Altair Airlines, based in Philadelphia, and Empire Airlines, of Utica/Rome, N.Y., and both hope to begin their operation next month.

Fokker says it sees a potential market of up to 180 propjects in the 50-seat category and 80 fanjets in the 80-seat class by 1985. The figures were based on a market analysis forecasting that commuter traffic would grow at an average of about 15 percent per year from 1979 through 1985. Last year, the commuters carried about 13 million passengers, 30 percent over 1978. That kind of growth -- a rise to about 30 million commuter passengers by 1985 -- will require the purchase of about 600 new aircraft altogether by the industry, Fokker said, although most of the need will be for aircraft seating 20 and 30. f