EVEN THOUGH frequent business travelers spend a good deal of time airborne, many suffer from fear of flying.

Boeing Aircraft released a study showing that nearly 25 million adult Americans are afraid to fly. One out of 10 who fly tolerates the experience in a state of fear. The fearful flyer averages one-third the number of trips taken by those who are not afraid to fly.

The main purpose of the Boeing study was to determine the economic impact of fear on the airline industry. In 1978, the U.S. airlines lost an estimated $1.9 billion as a result of fear of flying and that loss has increased as the cost of airline tickets has risen.

Most people experience anxiety in flight sometimes, but Boeing was interested in identifying those who either avoid flying altogether or are terrified at the prospect of an upcoming trip by air.

Women are more interested than men in seeking help to overcome their fear of flying, the study said. Females enrolled in therapy classes predominate (64 percent) and tend to be older (76 percent over 30 years of age versus 50 percent in the general population).

The fear of flying is more prevalent among blacks than whites, according to the survey, and those in lower socioeconomic groups are more fearful.

The statistics indicating a 9 percent drop in air travel due to fear of flying were gathered mainly from the middle-income group traveling for pleasure. However, as Boeing points out, there is no question that fear of flying is a serious problem among business travelers. The number of business trips taken and the revenue realized from these passengers makes fear of flying a major consideration in terms of lost airline revenue from commercial passengers.

It is difficult to analyze the business traveler and how his fear of flying influences how he conducts business. Those who are afraid to fly can't always avoid spending time in the air.

There also is a belief that many executives conceal their fears and manage to avoid getting on airplanes whenever possible. Often they maneuver their business dealings to eliminate a trip, make the other person fly to them or get someone else in their company to take the trip.

The Boeing report recommended more study be devoted to determining the economic impact on a particular company due to fear of flying.

Just why are people afraid to fly? Only about one-third of those surveyed by Boeing stated that they were afraid of dying in a plane. The majority of fearful flyers seemed to suffer from phobia-type fears. Aviophobia is more likely acrophobia, fear of height, or other unreasonable fears of darkness, water, crowds or confinement. The fear of height seems to be the prime reason people are nervous about flying.

Only 15 percent of those who have flown before consider flying to be dangerous as opposed to 29 percent of those who have never been in an airplane. d

Because there is no single reason for fear of flying, it is difficult to develop methods of combating the problem, according to Boeing.

In a fear of flying therapy session course developed by Pan Am, 51 percent of those enrolled indicated their anxiety developed after the first flight. Seventy-three percent indicated that fear increased with age.

Familiarity with the flight environment does seem to calm the nerves. The Pan Am course, which was taught by one of the airline's veteran pilots, T. W. Cummings, involved pyschology and also included taking the students on tours of airport facilities. The "final exam" was a graduation flight in a commercial aircraft.

Pan Am discontinued its fear of flying course. However, several similar courses are being conducted around the country. Cummings, retired from Pan Am, continues to run fear of flying seminars. In addition, he offers a mail order therapy course, which includes a booklet and audio cassette. His address is 2021 Country Club Prado, Coral Gables, Fla. 33134.

Boeing Aircraft's study praised the fear of flying courses as a method of assisting travelers get over the flight jitters, but cautioned the airline; industry that more data on the long-term effectiveness of this kind of therapy is required before airlines should lend their unqualified support to these courses.

Preliminary results of their effectiveness on the 6,700 people who have taken fear of flying therapy training is encouraging. Boeing reports that the Pan Am course, for example, had a 77 percent "cure rate" for those who completed the training.

Cummings' approach treats passengers' reactions symptomatically.

"When we get frightened, several things happen physiologically in response to psychological stress. Your gut tightens up, you perspire, breathing and heart rates increase," he said. "Only one of these automonic responses -- breathing -- can be controlled. When you control the breathing, it overshadows all the rest. We don't know just why it works, but it does."

Learning to control fear and to relax is the key to his fear of flying program. Because one must face and conquer fear with a clear head, Cummings opposes heavy drinking or tranquilizers, the standard treatments of the fearful flyer.

"Drinking distorts reality," he said. "To conquer fear, one must rationally experience." His seminar fee is $300, which includes the cost of the graduation flight. The home study course, including text material and audio cassette, costs $25.

Cummings offers anxious flyers a few nerve-settling suggestions:

Visit airports. Observe planes landing and taking off and learn all you can about flight operations.

Make your reservation early and arrive at the airport at least one hour before flight time.

Go to the airport with a friend who is sympathetic to your plight.

Find a comfortable seat in the departure lounge to sit, relax and breathe deeply before boarding the airplane.

On board, select a seat up front where it is smoother and quieter. Start a conservation with the person seated next to you. Recognize your anxieties as being okay, but don't focus on them.

Select reading material that will be distracting.

Keep your eyes open on takeoff. Don't sit rigidly in your seat. Wiggle your toes and move around in your seat.

Once the seatbelt sign is off, get up and move about. Don't resist the sights, sounds and movements on the plane. You are part of it now.