Airbus must be cheering.

CHICAGO (AP) -- The Boeing Co. delayed its 787 jetliner program again Tuesday, pushing back its expected debut in commercial service to the third quarter of 2009 as it continues to grapple with problems involving its supply chain and the need to redo work done by contractors.

The newest delays push the 787's schedule back approximately another six months and mean the aircraft touted for its potential to be more fuel-efficient than other large jets is now more than a year behind its original schedule.

The first test flight now isn't expected to take place until the fourth quarter as Boeing builds more time into the schedule to reduce the risk of further delays. The company had initially planned to begin test flights last August or September and deliver the first plane to Japan's All Nippon Airways this May -- a delivery it had recently rescheduled to early 2009.

The fourth delay with the 787, coming less than three months after the last one, further undermines Boeing's credibility on the much-hyped program and also is a setback to the more than 50 airlines that have placed about 900 orders for the top-selling plane. Buyers are likely to seek compensation for the delays.

The twin-engine widebody will be the first jetliner made largely of carbon-fiber plastic, which Boeing says will save fuel and be cheaper to maintain. But schedule delays with new jets are not uncommon, and Boeing also has had difficulties with a program that leans unusually heavily on overseas suppliers.

The company said that while significant progress has been made assembling the first airplane, it is rescheduling the first flight "due to slower-than-expected completion of work that traveled from supplier facilities into Boeing's final assembly line, unanticipated rework and the addition of margin into the testing schedule."

Boeing now anticipates delivering a total of 25 of the new airplanes in 2009.

"Over the past few months, we have taken strong actions to confront and overcome start-up issues on the program, and we have made solid progress," said Scott Carson, president and CEO of Boeing's Seattle-based commercial airplanes unit. "Nevertheless, the traveled work situation and some unanticipated rework have prevented us from hitting the milestones we laid out in January."

The company said research and development costs will likely increase because of the latest delay but it expects no change to 2008 earnings guidance. It said it will disclose more financial details when it reports first-quarter earnings on April 23.

Citing evidence of what it said is substantial progress, Boeing said it will power up the first aircraft by the end of June and also begin final assembly of the third and fourth 787s. It also revised the scheduling of the different 787 models, saying the larger 787-9 now will follow the original 787, with first delivery planned for 2012, while the shorter-range 787-3 that originally was pegged for a 2010 delivery will be pushed back behind the 787-9.

Analysts and customers had been expecting the latest delays. European rival Airbus saw delays of 18 months for its A380.