For the first time in a decade, U.S. manufacturers of small commuter planes and private aircraft reported an increase in business over the previous year. The number of aircraft delivered increased in 1988 by 5.3 percent, to 1,143 units, while the value of those deliveries increased about 40 percent to $1.9 billion, the General Aviation Manufacturers Association reported.

The results represent a major reversal of the industry trend of recent years, when sales have declined steadily. "We hope that the downward spiral has ended," said GAMA President Edward W. Stimpson.

But Stimpson added, "Although things are better, they are still not great." A few years ago some 18,000 aircraft were manufactured in a year.

The big increase in sales last year was in turbine-powered business aircraft _ larger business jets such as the Gulfstream IV and smaller ones built by Beech, Cessna and Learjet.

Several factors accounted for the stronger market, including increased demand from abroad aided by the falling dollar. Exports accounted for about a third of sales.

In addition, business demand for aircraft has increased as a result of the commercial airline industry's increased use of hub-and-spoke systems. While the hub-and-spoke system has helped fill commercial airliners and helped hold down airline fares, it also has added hours to the time that many business travelers spend getting from point to point.

Still other factors that are generating new orders for new aircraft are the needs of flight schools, which are trying to meet the growing demand of airlines for pilots, and the decline in the availability of used aircraft.