The crowd at America's airports has only begun to form. By 1993, it will have mushroomed into a formidable problem for transportation planners. ''Just close your eyes and imagine an airport you've used as a private citizen and think about twice as many people trying to use the facility,'' says Bill Parsons, chief program engineer in airport-aircraft compatibility for McDonnell Douglas. By 1995, ''I think you're going to find that we're looking at operating up to capacity (in many airports).''
The Federal Aviation Administration (FAA) estimates the number of passengers traveling each year will rise from the current 253 million to 465.3 million by 1993. The main reason, says Gene Mercer, chief of the FAA forecasting branch, is that more people, already accustomed to flying longer distances, prefer air travel over other forms of transportation for shorter trips as well.
The anticipated increase continues a historical growth trend at a slightly slower rate. However, it comes at a time when many observers say few, if any, new airports will be built.
''I would be surprised as a general rule if we are going to see any new airports in the next 10 to 20 years,'' says Ted McCagg, director of airport services for TRA, a Seattle-based design firm. Environmental constraints and higher costs make the building of new airports difficult, he says. ''If the traffic is going to increase in the next 10-year time frame, that increase is going to have to be handled at the airports of the present time.''
Already facing crowded facilities at some major airports, airlines have little option but to speed the pace at which passengers move through terminals. But in the airlines' quest for greater efficiency, a combination of competition and airport overcrowding could force them to slash some types of passenger services to a minimum. One possible result: passengers doing for themselves what the airlines currently do for them, such as carrying their luggage onto the airplane.
''There are a lot of ways you can reduce passenger handling,'' Mr. Mercer says. ''But you're stuck physically with a lot more people using the terminals.''
Not surprisingly, many airlines say they can handle the expected increase - and they offer various solutions to the crowding problem. But while these measures may ease the overcrowded situation for the airlines, they may be inconvenient for passengers, experts suggest.
Among suggested solutions:
* Adding new facilities to existing airports.
This is already being done at many airports, such as Chicago's O'Hare Field. There, an additional terminal building and a people-mover system are planned. The people-mover system (a moving sidewalk), experts say, will become more popular at large airports as a way to link satellite terminals. The satellite concept, which spreads terminal buildings farther apart and places them closer to the runways, has been used with apparent success at Atlanta International Airport. The less distance an airplane has to taxi, the less fuel it consumes.
But many airports, hemmed in by surrounding suburbs, cannot expand. And those that can expand may reduce airline fuel costs at the expense of passengers, who have to travel farther within the airport to board their plane.
''The airlines are so concerned about the short-term improvement of fuel conservation and (are) beginning to forget about passenger convenience,'' says James A. Meehan, associate vice-president of airport planning for Reynolds, Smith, and Hills, an architectural firm in Jacksonville, Fla.
* Increasing the use in major hubs of smaller surrounding airports.
This solution has been tried in several major hubs, such as New York, Chicago , Los Angeles, and Washington, D.C., with varying degrees of success. The system seems to work relatively well if the airport is the point of origin or the final destination. Critics point out, however, that transfer passengers forced to change airports as well as airplanes face a major inconvenience.
* Spreading airline schedules.
Scheduling more flights in the morning and late at night could alleviate pressure on the peak period of the day, suggests Walter Ericksen, a Lockheed staff engineer in airport compatibility. But passengers, who seem to prefer flying from 2 p.m. to 8 p.m., may have to change their ways.
The spreading schedules already are beginning, says Bruce Cunningham, vice-president of planning for New York Air. ''You notice a lot more flights scheduled at 7 o'clock in the morning.''
And the time may come when passengers flying during daily peak periods will have to pay a premium, suggests Mr. McCagg of TRA.
* Speeding up airline ticketing.
At Cleveland's Hopkins International Airport, United Airlines is experimenting with an automatic ticket vendor that sells the airline's Friendship Express. The express service is one way the airline is trying to cut costs by loading and unloading the aircraft as quickly as possible in order to reduce the time it spends on the ground.
New York Air, meanwhile, is using preprinted tickets to reduce costs and employee time spent writing out each ticket by hand. ''Our transaction time is a matter of seconds,'' Mr. Cunningham says. To further reduce costs, the tickets are collected on board the airplane by a flight attendant.
* Reducing baggage handling.
New York Air is also cutting corners by having passengers carry their own baggage onto the airplane. Other cut-rate airlines have gone further by charging passengers for each piece of luggage they bring on. ''Charging for them would make people far more conscious of what they bring,'' Mr. Cunningham says, an incentive that could reduce the total amount of luggage on each flight.
As yet, on-board ticketing and passenger-handled baggage are only being used by the cut-rate airlines. But Cunningham sees the day when all airlines will cut as many corners as possible to keep up with the competition. ''I think they will have to at some point,'' he says.
However, experts say air travel will remain essentially the same at least until 1995. And airline passengers until then may have to put up with what one observer calls ''an acceptable level of inconvenience.'' It may not be Cloud Nine, but these short-term adjustments by airlines may at least keep airline passengers in the air.