* Planemakers vying to fill gap between single and twin-aisle jets
* Crowded market segment could be worth up to $1 trn over 20 years
* Portuguese airline TAP takes delivery of first A330neo
By Tim Hepher
TOULOUSE, France, Nov 26 (Reuters) - Airbus delivered its first A330neo jet to TAP Portugal on Monday as it seeks to trump U.S. rival Boeing in the fiercely competitive battle at the lower end of the market for long-haul jets.
The face-off between the A330neo and Boeing 787 pits two generations of jetliner against each other in one of the most crowded but potentially lucrative parts of the aircraft market, predicted to represent $1 trillion in sales over 20 years.
Airbus said its upgraded A330neo, seating 250-298 passengers, would dovetail with the European planemaker's hot-selling A321neo narrowbody jet, which seats about 200, in the race to address a gap between single-aisle and twin-aisle jets.
Boeing is weighing up proposals to develop a new-generation jet carrying 220-270 passengers in a development analysts say could severely hurt the A330, the most profitable Airbus series.
The European planemaker is attempting to close its jaws around the same part of the market through a combination of the A330-800neo and the smaller A321neo, industry strategists say.
Sales of the A330neo have fallen short of expectations in the face of heavy competition from Boeing's 787, but the head of Airbus twin-aisle marketing predicted that it would hold its ground in the same way as the current A330 has done after Boeing was hit by production delays on the 787.
Despite weighing more than Boeing's 787 because of its metal structure, Airbus says the A330neo saves airlines money because of a more efficient wing.
Boeing, however, says the lightweight composite design of its 787 wins on economics despite its higher sticker price.
The aircraft delivered to TAP Portugal on Monday is the 298-seat A330-900neo, the larger of two versions developed by Airbus and one that dominates the tally of 242 aircraft on order.
The smaller A330-800neo took its first flight this month.
Airbus launched the revamped A330neo series in 2014 after failing to win as many orders as it had hoped for the A350-800, the smallest version of its own new-generation composite jet, the A350, which competes with most 787s and the larger 777.
The first A330neo delivery was delayed by setbacks at Britain's Rolls-Royce, which recently rescheduled deliveries of the Trent 7000 engine as it focuses on resolving difficulties with a sister engine that powers some Boeing 787s.
Leasing company Avolon financed the first TAP A330neo, with Singapore-based BOC Aviation involved in helping the Portuguese airline to finance progress payments ahead of Monday's delivery. (Reporting by Tim Hepher Editing by David Goodman)