All over America, airline passengers have begun to collect something other than baggage tags and complaints.

The spur is the latest airline marketing tool -- the bonus program -- that awards free or reduced future travel to customers who collect enough segments, points, coupons or mileage on current flights.

The promotions are aimed at the airlines' frequent fliers, but even not-so-frequent travelers can take advantage of some of the proliferating programs.

Perhaps the most generous of the current programs, and certainly one of the easiest to understand, is Northwest Orient Airlines' "Free Flight Plan." For taking 10 one-way flights -- five roundtrips -- on Northwest, a person can get a free economy-class roundtrip ticket to any of Northwest's U.S. destinations, including Hawaii and Alaska.

Like most of the other airline programs, a person participating in the Northwest program can collect the award at the first stage or keep on going. NWO's second stage, 20 one-way segments, yields a free first-class roundtrip ticket to any NWO domestic city; for 30 segments, a traveler can get a free executive class roundtrip ticket to any NWO international destination, including Europe and the Orient; for 40 segments, a free first-class roundtrip ticket to a Northwest international destination is yours.

Northwest's rules are simple and straightforward: all its domestic flight segments traveled between July 15, 1981, and June 30, 1982, count toward the bonuses, as long as the fare of each segment is at least $75. No prior enrollment in the plan is required. Travelers keep track of their own travel in a brochure the airline distributes, turning the log and ticket coupons over to Northwest when enough segments are collected.

An unusual part of Northwest's program includes a bonus for the travel agent or secretary booking a boss's flights. The person making the travel arrangements gets a free flight bonus equal to the award given the traveler.

Delta Air Lines and Republic Airlines also have programs based on the collection of segments. Delta's "Frequent Flyer" program, which requires travelers to sign up ahead of time, is less generous than Northwest's. The collection of 10 domestic flight segments on Delta allows a person to have his or her one-way or roundtrip coach ticket upgraded to first class, a common first-stage award for many of the programs.

Collecting 20 Delta segments entitles the traveler to a 25 percent discount on a ticket, and 30 segments gets a 50 percent discount. At 40 segments, the Delta passenger can get a free roundtrip coach ticket or a 75 percent discount on a first-class ticket; for 50 segments, a free first-class roundtrip ticket is offered, and for 70 segments, two roundtrip coach tickets are the prize.

The bonus tickets are good on Delta's routes within the continental United States, Bermuda, Bahamas and Puerto Rico but not on its European and Canadian routes.

Flights flown before the end of 1982 count in the program. To get a traveler started in the program, Delta allows up to five segments on Delta or another airline between Jan. 1, 1981, and Sept. 1, 1981, to apply to any of the bonus options. Beginning Sept. 1, first-class segments have counted as two segments.

Republic also counts segments for its "Frequent Flyer Passport Bonus" program, but a person must fly six one-way trips, after July 1, l981, on Republic before being eligible for membership in the program. For signing up, Republic gives a 50-percent discount on a future Republic flight. Frequent flyers also receive a special passport to carry with them that is validated every time a Republic flight is taken; trips taken through the end of 1982 count. A free roundtrip on Republic's domestic system can be awarded after nine one-way segments are flown.

All the programs vary in their details and rules, and they can change as the programs move along. Some of them will grant double mileage or points for certain periods of time -- for instance, on certain routes on which they want to encourage travel. Some don't count flights using some discount fares. Some of the programs' awards are also tied in to discounts for hotel rooms and rental cars.

Both Braniff International and Continental Airlines are using a point system for their programs but the similarity stops there.

Braniff's "Travel Bonus Bonanza" gives travelers points -- ranging from one to 21 -- for flying its routes between June 1, 1981, and May 31, 1982. The Washington-Dallas route, for instance, yields six points each way normally, although Braniff is doubling all points through Nov. 15. Extra bonus points are awarded for flying first class, and the travel of accompanying family members with the same last name can earn points that add to the traveler's total.

For 30 points, a person is allowed to purchase a first-class roundtrip ticket on Braniff for the price of a coach ticket on any of its domestic routes or can have a one-year membership in its airline club. With a minimum of 75 points, a person can begin claiming discounts or free tickets on Braniff's routes. For a free roundtrip between Washington and Honolulu between now and May, for instance, a person would need a total of 125 points.

No prior signup is necessary; participants in Braniff's program save their ticket receipts or photocopies of them and boarding passes and keep track of their point progress in the flight log printed in a folder describing the program.

Under Continental's program, called "Flight Bank," travelers earn travel points that are deposited into an account everytime a Continental flight is taken using a full fare coach or first-class ticket, from July 1, 1981, through Dec. 31, 1982. For instance, a traveler collects 400 points for flying from Washington to Denver, 100 points for flying between Houston and San Antonio.

Once a minimum of 1,000 points is collected, a traveler can begin to make withdrawals from the account that serve as credit checks good for travel on Continental. For collecting 1,000 points, for instance, a traveler gets $285 credit for travel on Continental. A person can withdraw the travel points collected at 1,000 or 2,000 or let the account build.

Travelers must enroll in this program by first flying a Continental flight; when the account is first opened, a traveler is entitled to upgrade a coach ticket on Continental for one in first class.

Mileage forms the basis of the programs offered by American, Eastern, Trans World and United airlines. Although each program differs in its details, in general each time a passenger takes a flight, he or she is credited with at least the actual mileage flown, sometimes more. Each requires enrollment of some sort because company computers keep track of the mileage.

Under American's "AAdvantage" program, a person who has logged 12,000 miles in the air on American may upgrade a coach roundtrip ticket to first class anywhere American flies, or go on to the next level. For 20,000 miles, one gets a 25 percent discount on a roundtrip ticket; 30,000 miles yields a 50 percent discount; 40,000 miles gets a 75 percent discount. At 50,000 miles, one can get a free first-class roundtrip ticket anywhere American flies, including Mexico and the Caribbean, plus a free first-class upgrade of a coach ticket for a flying companion. The reward at 75,000 miles is two free first-class tickets to any American destination. A person can collect mileage only within one year of the first use of American's program.

United's "Mileage Plus" program awards are similar to American's although a traveler can get the first-class upgrade at 10,000 miles instead of 12,000. (Eastern's and TWA's awards also start at 10,000 miles.) United's bonuses stop at 50,000 miles with the award of a free first-class roundtrip ticket to any of its U.S. or Canadian destinations, along with the free first-class upgrade of a companion's coach ticket. United gives every enrollee 1,000 bonus miles to get started. Mileage can be accumulated through Dec. 31, 1982, in United's program. Likewise Eastern's and TWA's programs.

Trans World's "Frequent Flight Bonus" program operates in a similar fashion, but its bonus awards apply to its farther-flung international destinations as well as domestic. After collecting 50,000 miles, a traveler can get a free first-class roundtrip ticket for any TWA destination, including Europe. At 60,000 miles, one can get two free economy roundtrip tickets -- one for the participant and one for an eligible family member. TWA also gives starters 1,000 free miles, and grants an additional 25 percent of a flight's mileage for flying on a first-class ticket.

Like the other mileage-based programs, Eastern's is similar but, at 40,000 miles, the participant can get a free coach roundtrip ticket or a 75 percent discount on a first-class ticket. At 50,000 miles, a free roundtrip first-class ticket is available anywhere on Eastern or a 50 percent discount for two on its week-long vacation packages in Florida, Mexico and the Caribbean. At 70,000 miles, the program awards two free coach tickets on Eastern. Travelers can be enrolled in the Eastern program the first time they fly on the airline. Eastern gives travelers a minimum of 1,000 miles for every flight they take; for instance, Air-Shuttle flights, which are less than 1,000 miles, would contribute 1,000 miles to a person's total.

Although hurdles for awards of free tickets may sound steep, they aren't for the frequent business passengers and professionals who are constantly flying.

Western Airlines, a Los Angeles-based airline with limited Eastern routes, has a "$50 Travel Pass" that rewards frequent travelers for flying on routes from 13 of the cities it serves. Passengers flying these routes carry a wallet-sized travel pass card that is machine validated each time a passenger boards a travel-pass flight. Normally, after five validations on one card, the pass is worth $50 toward travel on Western. During October, the passes are being double-validated each time they are presented.