Citing adverse market conditions, Northwest Airlines wants to delay its planned service from Seattle-Tacoma International Airport to Beijing, China, from March 2009 to March 2010.

Northwest Airlines, the subsidiary of Delta Air Lines, wants U.S. Department of Transportation approval to delay the route's start-up date without losing its rights to the route.

Bookings between the U.S. and China have dropped by almost a third in the past year, the airline told the DOT.

Northwest also wants to delay service between Beijing and Detroit by several months as well.

The airline's Detroit-to-Shanghai route will also be suspended between Mar. 28 and Jun. 3, said Anthony Black, Delta spokesman.

Northwest had lobbied hard for that route, finally getting approval from regulators about a year ago.

The announcement comes a month after Northwest said it will drop its Seattle-to-London non-stop flight next year, less than six months after inaugurating the service. The non-stop flights will end on Jan. 8.