Already beset by higher ticket prices, airlines passengers may now be hit with additional travel costs: fees for baggage that up to now has been carried for free by the airlines.

Braniff International yesterday began imposing tighter baggage-weight restrictions on all of its flights to and from Latin America. Passengers on these flights will be forced to carry a lighter load if they don't want to pay extra for their baggage. Where they used to be able to carry up to two 70-pound suitcases for free, they will be allowed only two 50-pound bags.

Pan American World Airways is considering imposing even tighter limits, beginning Oct. 1, on all of its international and domestic flights.

Under a proposal recently approved by the Civil Aeronautics Board, Pan Am wants to limit its discount passengers to one free piece of baggage, weighing no more than 50 pounds. Currently, all Pan Am passengers are allowed two free bags, weighing no more than 70 pounds each.

The precise fee for the second bag will depend on the length of the trip. For a Washington-London flight, the cost for each extra bag would be $49 one-way. For a Washington-New York flight, the cost per bag would be $7 one-way, the same fee charged for overweight luggage before thereduction.

Pan Am officials say the airline must change its rules to solve an increasingly troublesome predicament where it is unable to carry all of its passengers baggage. On its South American flights, for example, airline officials say many travellers come to the U.S. and buy dozens of small appliances, such as televisions and stereo sets, and then expect them to be shipped back with them as normal baggage.

"We have people showing up and fillng up the belly of the aircraft before all of the people with luggage have checked in," said Pan Am spokesman Merle Richman.

This problem also occurs on flights to Africa and some points in the Far East.

Yet, because Pan Am wants to impose tighter baggage limits on all of its flights, its proposal has drawn sharp criticism from consumer groups.

"If there really is a documented problem, a capacity crunch, then the airline really ought to be able to move to solve it," said Cornish Hitchcock, legal director for Aviation Consumer Action Project. "But Pan Am is not trying to limit its restrictions to its problem routes. It is doing it across the board and that's what we object to."