Airline managements, which were long thought to be operating as a pack, are beginning to use different approaches to attract passengers.

Two recent examples:

American Airlines and Trans World Airlines have decided to provide segregated seating and special seat selection, ticketing, check-in and meal services for full-fare passengers. "It's about time the airline industry realized its best customers deserve its be service," an advertising pitch from TWA begins.

Delta Airlines has decided not to seek the fare increases - of up to 4 percent - that other airlines have asked the Civil Aeronautics Board to approve, effective in November. In fact, Delta has told the CAB it will hold the line on coach fares and wants permission to lower its first-class fares. Delta asked to reduce the mark-up on first class over coach from 30 percent to 25 percent on short trips and 20 percent on long trips (800 miles or more).

How all the airlines are going to react to the initiatives of the others is unclear: at least one, Eastern Airlines, has said it won't foid it won't follow the three-class-service plans of American and TWA. Segregating first-class, full coach fare, and discount passengers is costly, requiring some alteration of the plane, check-in counters, and additional personnel. According to Eastern's president, Frank Borman, the plan causes an "operational headache" Eastern tried it on its New York-Miami route.

But American and TWA officials contend that the increased traffic drawn to the airlines by the popular discount fares have inconvenienced the full-fare passenger, who often travels on business frequently and provides a major share of the airlines' revenues.

"Business fliers are an airline's bedrock customers," an American ad exclaims. "But though they usually pay full fare, they don't always get fullfare treatment."

Both are promising the full-fare passenger a special coach section where their seatmates also will be full-fare passengers - with the implicit promise of no crying children. When there are empty seats on the plane, they probably will be in your section, the ads promise.

Full-fare passengers also will be able to select seats on the to-and-from flights when reservations are made, get boarding passes ahead of time, and such things - depending on the airline - as separate check-in counters at major airports, meals served before others, and more space for carry-on luggage.

The plans are subject to CAB approval, which is expected tomorrow.

Although the two airlines seem to be complicating their service obligations, they have moved to simplify their fare structures. TWA and Americans both asked the CAB for permission to replace a complicated fare structure - with more than 15 promotional offerings - with seven basic fare options.

The seven are first-class, coach, night coach (with discounts of up to 20 percent), Super-Saver (with discounts of up to 50 percent for tickets bought 30 days in advance for stays of 7 to 45 days), a new fare with discounts of up to 30 percent for tickets bought seven days in advance for trips 7 to 45 days in length, a group fare and a tour package fare.

The new fare structure eliminated a variety of discount fares, including a senior-citizen one-day standby fare.

All the airlines have not followed suit, and generally have not formulated their response to Delta's fare-holding initiative. They are "studying" it.

It is possible that some will raise their fares to the level the CAB will approve and see what happens. This recently occured in California when the state regulatory body authorized fare increases for California routes. Pacific Southwest Airlines - which became famous on low-fare, full-plane service - raised its fares, but federally certificated Western Airlines - in a bid to increase its market share - chose not to follow suit.