* Air Berlin CEO says in talks with three aviation firms
* Aims for deal with at least two buyers by end-September
* Lufthansa, Eurowings, Condor to get best slots - RND
* Transport minister sees opportunity for German firms (Recasts, adds German transport minister comment, details on slot auction)
FRANKFURT, Aug 17 (Reuters) - Insolvent German airline Air Berlin aims to strike deals to sell assets to two or more buyers by the end of September, before a government loan keeping its planes in the air runs out, its chief executive said.
The group is in talks with a total of three aviation firms, including Lufthansa, German newspaper Frankfurter Allgemeine Zeitung (FAZ) quoted Thomas Winkelmann as saying in its Thursday edition.
All three are "reputable in terms of their finances, sufficiently large to offer Air Berlin a secure future and are interested in keeping Germany as a base of operations", he said, without naming any of the interested parties.
Air Berlin, Germany's second-largest airline, filed for bankruptcy protection on Tuesday after key shareholder Etihad Airways withdrew funding following years of losses, leaving valuable runway slots up for grabs.
The insolvency comes with thousands of Germans enjoying summer holidays, and just ahead of a September general election.
The German government granted a bridging loan of 150 million euros to allow Air Berlin to keep its planes in the air for three months and secure the jobs of its 7,200 workers in Germany while negotiations go on.
The move offers Lufthansa and rivals a chance to acquire slots at airports such as Berlin Tegel and Duesseldorf, with Germany's largest airline keen to defend its domestic position against expansion by low-cost rival Ryanair.
According to Winkelmann, the negotiations also include assets of Air Berlin unit Niki, which Etihad had agreed to buy for 300 million euros ($354 million) earlier this year.
RedaktionsNetzwerk Deutschland (RND), a group which represents German newspapers, cited government sources as saying that Lufthansa, its budget carrier Eurowings and Condor would likely snap up Air Berlin's most valuable landing slots.
It said a few slots could also go to Ryanair, which has filed a complaint with German and European Union competition authorities over the insolvency process, which its chief executive describes as a "conspiracy".
Lufthansa has confirmed it is in talks to take over parts of Air Berlin's business, while a source has said easyJet was also part of the negotiations.
Thomas Cook's German airline Condor said on Wednesday it was ready to play "an active role" in Air Berlin's restructuring, without being more specific.
Germany's Transport Minister Alexander Dobrindt said the asset sales were an opportunity for the country's aviation sector to bolster its footprint.
"The opportunity should be seized to strategically position the 140 aircraft, the capacities and the employees of Air Berlin and strengthen the position of Germany's aviation sector in the international market," German daily Bild quoted him as saying. ($1 = 0.8485 euros) (Reporting by Maria Sheahan; editing by Robert Birsel and Alexander Smith)