* Launch expected at next week's Farnborough Airshow
* Airbus upgrading its biggest-selling wide-body jet
* Upgrade amid poor sales of new A350-800 (Adds details, analyst quote)
By Tim Hepher
LONDON, July 11 (Reuters) - European planemaker Airbus will both revamp and rebrand its A330 passenger jet at a launch expected to kick off next week's Farnborough Airshow, people familiar with the matter said on Friday.
The A330-800neo and A330-900neo will be upgraded versions of the A330-200 and A330-300 respectively and include some cabin improvements and 400 nautical miles more range, while Airbus will also study ways of improving the use of floor space.
As reported by Reuters in June, next week's announcement will highlight at least 14 percent greater fuel efficiency and a new version of the Rolls-Royce Trent engine, but will also accelerate the end of the poor-selling A350-800.
Airbus declined to comment.
"We do not comment on the usual air show noise," a spokesman said.
Leasing companies are expected to be among the initial buyers, but it was not immediately clear whether the launch would be subject to further board approvals.
In service since the 1990s, the A330 is Airbus's biggest-selling wide-body jet.
Sales have been stronger than expected recently due to delays in producing the newer Boeing 787. But that advantage is evaporating and Airbus now wants to refresh the design in order to defend its position in the lucrative 250-300-seat market.
Its arrival is expected to spark greater price competition for sales at the lower end of the market for wide-body jets.
Anticipating an air show move by its rival, Boeing said on Thursday the A330 upgrade papered over a series of strategy changes after Airbus counted on its future A350-800.
Sales of that jet have been disappointing, with just 34 left on order.
The name change appears designed to smooth that transition, but Airbus is also keen to distinguish between the current A330, which will remain on sale for regional trips, and the "neo" which will be pitched as a step towards the newer A350.
There had been some speculation that Airbus might call it after the A350 for that reason, but borrowing the name of a different aircraft family can pose branding and certification problems or clash with airlines' pilot union agreements.
The engine, a modified Trent 1000-TEN, will be dubbed Trent 7000, sources said, confirming a Wall Street Journal report.
The numerology of aircraft models is virtually a science in itself and is watched closely in some key markets such as China. Boeing also uses the 800/900 tag, or more recently 8/9.
"Rebranding the A330 (and) ... adopting the more modern -800/-900 speaks to the significant upgrade of the airplane," said aviation analyst Scott Hamilton.
"It speaks to adopting new technology and is consistent with the sub-type branding of the A350."
Details are also emerging of what the A330 redesign, which is still under wraps, will look and feel like to passengers.
The A330neo will have between 252 and 306 seats, slightly more than the Boeing 787-8 or 787-9 and 10 more than the current type of A330, according to an airline briefing seen by Reuters.
In terms of performance, airlines have been told the smaller version of A330neo will have the same range as the Boeing 787-8, while the larger variant will lag the 787-9 by 1,000 miles.
Airbus says most airlines don't need the 787's range or some of its widely publicized features such as large windows. Boeing says its carbon-fibre jet is more comfortable and efficient, whatever length of trip is considered.
(Editing by Mark Potter)