American Airlines says it will let frequent fliers use miles to book one-way trips for half the miles of a round trip.

The airline will also let customers redeem miles to fly one leg of a round trip in first-class and fewer miles to fly in coach on the other leg. Officials at American, which developed the first frequent-flier program nearly three decades ago, plans to announce the changes Monday and put them into effect shortly.

They say American is the first major U.S. airline to offer a one-way award ticket at half miles. It's hard to know how many people would use miles for a one-way trip — parents driving a child to college and flying home might — and American officials didn't offer any estimates.

"I think more customers will claim more awards," said Rob Friedman, president of marketing for American's frequent-flier program, AAdvantage. "I think there will be more spontaneous kinds of trips."

Last year, AAdvantage members redeemed 3.1 million trips in 2008, up from 2.6 million in 2007. Those who track airline reward programs said people used miles last year to avoid fares that rose quickly when oil prices spiked.

The changes American will announce Monday also could reduce the need for reservations agents because customers will be able to go online and book some trips that until now could only be booked through an agent — incurring a $20 fee. An example is a multi-city itinerary in which a passenger — typically on business — would stop in two or more cities before returning home.

Friedman said agents would still be an option to handle complicated itineraries.

The idea of using more miles on one leg of a round trip than the other could appeal to business travelers.

Frank Schnur, the vice president of global advisory services at American Express Business Travel, said companies want key employees to keep traveling while controlling costs. He said one way to do this is for employees to fly first-class to a meeting in Europe so they arrive rested, but fly home in coach.

American officials said they will also upgrade their Web site to let customers book award trips in Spanish. They said they are considering adding other languages, perhaps French or German.

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