* Berlin airport delay hits German reputation for efficiency
* City's mayor blamed by many for airport's fifth postponement
* German regulations and bureaucracy part of problem
BERLIN, Jan 7 (Reuters) - A fifth postponement of the opening of Berlin's new international airport has tarnished Germany's reputation for efficiency and threatens to ruin the high-flying career of the city's mayor Klaus Wowereit.
Already 20 years in the planning, Berlin's new 4.3-billion euro ($5.61 billion) Willy Brandt International Airport has had to push back its opening from 2011 to June 2012, then to March 2013, then to October 2013 and now to 2014, a source familiar with the plans told Reuters on Sunday.
The delays, caused by red tape and, latterly, problems with the fire-safety system, have turned the airport and its city into the butt of nationwide jokes. Authorities fear the latest hold-up could harm the global reputation of German engineering.
Berlin's Tegel airport - one of three in the city that Willy Brandt is meant to replace - was built in just 90 days during the Cold War.
Sixty years after that feat, the protracted struggle to open the airport has exposed the inefficiencies of a country weighed down by regulations and layers of bureaucracy.
Construction only began in 2006 after a tortuous 15-year planning and approvals process for the air hub in the southeast corner of the city.
Even though the airport is jointly owned by the federal government, Brandenburg state and Berlin, most of the blame for the debacle has fallen on Wowereit - once one of Germany's most popular leaders.
'WOWEREIT MUST GO'
The Social Democrat, who chairs the airport supervisory board, is under fire over allegations he covered up news of the latest delay for the last three weeks, prompting calls for his resignation.
"Wowereit has withheld information about new problems at the airport and he's a liability," said Ramona Pop, a leader of the opposition Greens in the city-state assembly. She said the assembly should vote him out. "He's harming Berlin's interests."
The Greens' national co-leader, Juergen Trittin, intervened to tell Wowereit to step down: "It's over, Klaus."
But Wowereit won a potentially vital lifeline from his own party on Monday.
"Why should he resign? I can't see any reason for that," said the chairman of the Social Democrats (SPD), Sigmar Gabriel.
"If the technical experts say the airport opening has to be delayed, what else can the supervisory board chairman do?" Gabriel added.
The calls for Wowereit to go are not likely lead to his immediate exit. But the pressure against him is growing in the media and his standing in opinion polls has plunged in recent months.
Wowereit has been mayor since 2001. He became a national celebrity by coming out as gay during that election campaign just as one newspaper was planning to expose his sexuality.
At the height of his national popularity in 2006, Wowereit was one of only a handful of SPD state leaders capable of winning their elections and many saw him as a future chancellor.
Wowereit, 59, took over a city deeply in debt and struggling to overcome decades of Cold War divisions. With high unemployment and low wages, Berlin was also struggling to find its place in reunited Germany.
"Berlin is poor but sexy," Wowereit once said, giving the city a hip slogan that stuck and helped him win re-election three times. That image helped lure film and music companies as well as tens of thousands of artists and writers to Berlin even as the city's jobless rate fell and the cost of living climbed. ($1 = 0.7666 euros) (Reporting By Erik Kirschbaum, editing by Gareth Jones and Andrew Heavens)