By Karolos Grohmann

RIO DE JANEIRO (Reuters) - With the Rio de Janeiro Olympics in imminent danger of cementing a reputation as the most trouble-plagued Games in recent history, organizers are struggling to convince the world of their good intentions as problems increase by the day.

Games chief spokesman Mario Andrada, an experienced journalist, has had the unenviable job of delivering bad news to a global media audience on a daily basis with organizers unable to make problems go away.

A fire at the mountain bike venue that damaged signage among other things on Monday was the latest issue to hit the Olympics, already grappling with poor attendances, a lack of cash, chaotic transportation, a worrying shortage of volunteers, crime and a widespread feeling of malaise sweeping across the Olympic parks.

The king of Olympic sports -- athletics -- has been the latest casualty with the stadium consistently showing empty seats, thousands on Monday evening alone.

"We understand it is a big stadium. We understand more seats should be filled," Andrada told reporters as his daily briefing was once more peppered with critical questions about organizers' ability to deliver on promises of full venues.

Andrada has had to answer the same question from day one but has failed to provide a convincing response. Media representatives have even compared him with his Beijing 2008 Olympics counterparts, notorious for their ability to dodge tough questions.

"There are several reasons according to our own research about how the stadiums, especially the track and field stadium, doesn't look as full as it should look," Andrada said.

"Long sessions, no-shows, tickets sold and people don't show up. In some venues, people... leave, especially to get food. This is a matter that has been discussed from day one here," he said.

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"It worries us but in a constructive manner," he said cryptically with the Games five days from finishing.

The straight-faced Andrada also admitted what was clear from the start of the Games, that volunteers had failed to turn up in large numbers.

"We did have some lower number in volunteers attending in some critical activity. We went very close to 50 percent attendance in some areas.

"We see the main gaps in long hours ...or volunteers having to say no to people... and not ready to cope with that. We have to worry about the second week."

With the Games at risk of leaving a legacy of missed opportunities instead of being remembered as the spectacular first South American Olympics they were supposed to be, Andrada tried to explain what had led to the shortcomings.

"Before the Games we were battling in a complex environment. Political and economic. Low ticket sales tell this tale.

"Communication could be better but that is not the reason to explain why stadiums are looking empty in some sessions," he said.

With five full days of action left few believe Rio organizers can turn these Games around.

"We understand that some athletes are disappointed. We understand that the media is worried," Andrada said.

"We are worried but we are working within the framework of a Games that are privately funded... despite the problems that we're having in stadiums not looking full we are going after this problem trying to solve it."

(Editing by Clare Fallon)