ATLANTA - Delta Air Lines said Thursday that it will adopt a popular feature of Northwest Airlines' frequent-flier program, as it aims to merge the two reward systems by the end of 2009.

Delta will allow its travelers to qualify for elite status by flying a certain number of segments, in addition to flying enough miles. The segment rule comes from Northwest, which flies many short routes around the Midwest that connect through its hubs. So, a single flight from, say, Minot, N.D., to New York with a stop in Minneapolis would count as two segments.

Delta said the new rule will begin Jan. 1. Delta acquired Northwest in a deal that closed Oct. 29, and is working to integrate the two carriers over the next one to two years.

Delta said it will add a third tier to Northwest WorldPerks awards, which has two tiers for domestic travel, with tickets generally available for 25,000 miles and 50,000 miles flown. Delta's tiers for domestic travel are 25,000, 40,000 and 60,000 miles.

Delta also said all its frequent fliers will continue to earn at least 500 miles per flight, even when their flights are shorter. Some airlines have begun awarding the actual miles for short flights.

Travelers on Delta who have SkyMiles accounts as well as WorldPerks accounts will be able to transfer miles between them beginning early next year.

The carrier expects to entirely merge the two programs late next year.

ASSOCIATED PRESS