FORT WORTH, Texas, July 23 (Reuters) - American Airlines said it began selling tickets this week for new shuttle flights linking Boston, New York and Washington this fall, joining two rivals serving the popular routes through its American Eagle partner. AMR Corp.'s (AMR) American Eagle unit will use 44-seat Embraer (EMBR4) jets to compete against US Airways Group Inc.'s (U) Airbus A319s and A320s, which seat 124 or 150 passengers, and Delta Air Lines Inc.'s (DAL) comparably sized Boeing 737-800s. American's more modest service will offer 10 flights a day between New York's Laguardia Airport and Boston's Logan Airport and between Laguardia and Reagan National Airport just outside Washington. The carrier already offers five flights a day between Boston and Washington and is adding a sixth on Aug. 1. American Eagle's Boston-New York service starts on Sept. 24 followed by New York-Washington a week later. The shuttle flights will offer leather seating, like Delta's and US Airways', with three seats per row, separated by a single aisle. Delta currently offers 17 daily flights between New York and Boston and another 15 New York-Washington flights. US Airways' shuttle runs 16 daily New York-Boston flights, 15 from New York to Washington and 14 between Boston and Washington. AMR Corp.'s fleet, including TWA, is the nation's largest. Delta is the third-largest U.S. carrier and US Airways No. 7. ©2002 Reuters Limited.