* Condor eyes double-digit number of planes - source
* Lufthansa set out concept to Air Berlin on Wednesday
* EasyJet interested in up to 40 planes - paper (Adds details on rival bidders)
BERLIN, Aug 24 (Reuters) - Thomas Cook's German leisure airline Condor is interested in taking on a number of planes from insolvent Air Berlin, a source familiar with the negotiations said on Thursday.
The leisure airline is "in the process of preparing a concrete offer", the source said, adding Condor was interested in mainly short-haul routes, and also some long-haul ones.
Air Berlin, Germany's second largest carrier, filed for insolvency last week after major shareholder Etihad pulled the plug on funding.
The race is on for interested parties to agree a deal for parts of its business, including planes and crew, which would bring access to take-off and landing slots at airports such as Duesseldorf, Berlin Tegel, Munich and Hamburg.
German flagship carrier Lufthansa, which was first to talk with Air Berlin, on Wednesday said it had presented a term-sheet to the insolvent carrier, setting out its interest in taking over parts of the Air Berlin group.
A source had said Lufthansa was interested in Austria-based Niki, which flies routes to tourist destinations from Germany and Austria, plus other parts of the business.
Air Berlin's planes are currently being kept in the air thanks to a 150 million euro ($177 million) government loan. But if the money runs out and Air Berlin is grounded, the slots go into a pool where they will be divided up among airlines, a process that industry experts say would play more into the hands of Ryanair and easyJet.
Thomas Cook repeated an earlier statement that it stood ready to play an "active role".
Its interest in a "double-digit" number of planes was first reported by Sueddeutsche Zeitung.
EasyJet is also interested in up to 40 planes, with slots in Berlin and Hamburg, Handelsblatt reported. The British budget carrier declined to comment.
Ryanair has also said it would be interested in a bid for the whole of Air Berlin, as has German aviation investor Hans Rudolf Woehrl.
Woehrl said on Thursday he had been invited to talks with Air Berlin next week.
Meanwhile, Lufthansa's budget unit Eurowings seemed to be making an early attempt to attract any Air Berlin staff keen to find a new job while negotiations are still ongoing.
Eurowings on Wednesday announced a recruitment drive, saying it was seeking around 200 pilots and 400 cabin crew qualified to fly and crew A320 planes. It did not specifically mention Air Berlin in the announcement on its website.
($1 = 0.8481 euros) (Editing by Maria Sheahan and Mark Potter)