SEATTLE — Starbucks said Tuesday it’s launching its mobile order program in more than half of the stores it owns in the United States.

The move follows an initial pilot launched last December in Portland, Ore., and expanded three months later to some 600 locations across the Pacific Northwest. The latest expansion means that an additional 3,400 stores in 21 states, from Texas to Wyoming and Arizona to South Carolina, have it. So do stores in South and Central California.

Mobile ordering and pay is a key initiative for Starbucks, which seeks to lure more customers into using its app and reward program, whose members tend to spend more at its cafes and visit more often.

The mobile ordering procedure – through which a customer can place an order online through a smartphone and pick it up directly at the counter a few minutes later – also helps cut down time spent in line at rush hour. Lengthy waiting times have become more of a problem as Starbucks increases the complexity of its menu with pastries and lunch options.

The Seattle coffee giant says it plans to deploy the mobile order system in the rest of its company-owned stores in the U.S. later this year.