CHICAGO — 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.