Lufthansa CEO warns Brexit "crisis" would hit European travel demand

* CEO warns Brexit could hit European air travel

* Lufthansa preparing for possible Brexit crisis

* German airline reduces seat growth plans (Adds background on rivals, outlook)

By Tom Käckenhoff

DUESSELDORF, Germany, May 19 (Reuters) - A British exit from the European Union could be a "crisis" that would hit economic growth in the region and lower demand for air travel, the head of German airline Lufthansa warned.

Britons will vote on June 23 on whether their country should remain in or leave the 28-member bloc and many business have spoken out in favour of remaining in the EU.

"I am certain that Brexit would result in lower growth in Europe and that would lead to less demand from customers," CEO Carsten Spohr said at an event late Wednesday in Duesseldorf.

"We're preparing for Brexit just we would any other possible crisis, and a crisis is how I would describe it. I hope it won't come to it though."

Irish low-cost carrier Ryanair has threatened to withdraw some investment from the UK in the event of Brexit but Spohr said Lufthansa's investment in Britain was small and the carrier had no plans to reduce it.

Airlines, which have benefited from lower oil prices, are already grappling with pressure on ticket prices as a result of structural overcapacity in the industry.

Spohr said Lufthansa, which had planned to raise the number of seats on offer by 6.6 percent this year, now intends to bring that to below 6 percent, without specifying the exact figure.

Lufthansa will ground three long haul planes on loss-making routes after the summer, he said.

Delta Air Lines (NYSE: DAL - news) on Monday trimmed its growth plans and said it will defer the delivery of aircraft. (Writing by Victoria Bryan; Editing by Alexander Smith)