Delta Air Lines Inc. said Friday that it will start adding airport fees to its ticket prices after previously absorbing them, a move that could boost fares nationwide if matched by rivals.

Delta, which is operating under bankruptcy protection and lost more than $500 million in January and February, said passengers could pay $3 to $4.50 more each way on flights that connect through airports charging the fees.

If rivals match the move, it would be the latest in a series of fare increases this year by U.S. carriers, which are trying to climb back to profitability after several years of losses.

But Northwest Airlines Corp. tried adding the fees, called passenger facility charges, to its ticket prices last year, only to retreat when the move was not matched by all of its rivals, notably Continental Airlines Inc.

"Continental did not go along in the past. The key is, will they go along this time," said Terry Trippler, an analyst with travel Web site Cheapseats.com. "For the passenger, it's something they have been getting free, technically, that they shouldn't have been all this time."

Continental, whose main hub in Houston does not have a passenger facility charge, could not immediately be reached for comment.

Delta, the No. 3 U.S. airline, said such fees, levied by airports to pay for improvements, added up to as much as $18 for a round-trip itinerary.

Airlines began absorbing the fees to be competitive with rivals flights that connected through airports that did not charge such fees or that were direct.

"The changes we are announcing today allow us to more accurately display the full costs of government fees imposed on certain connecting itineraries while at the same time allowing us to collect the appropriate revenues to cover a portion of these costs," Gail Grimmett, Delta's vice president for revenue management, said in a statement.