By Erik Kirschbaum

BERLIN (Reuters) - Anti-doping controls at the Beijing Games will be the most extensive ever implemented, said International Olympic Committee (IOC) vice president Thomas Bach.

In an interview with Reuters, Bach also said the Beijing air may not be as clean as expected and he hoped Chinese authorities would redouble their efforts to reduce pollution before the Games started on August 8.

Bach, the head of Germany's National Olympic Committee who is also chairman of the IOC's disciplinary commission, said anti-doping screening had improved since scandals plagued the 2004 Athens Summer Games and the 2006 Turin Winter Olympics.

"The Beijing Games will be by far the most rigorously controlled ever and the most stringently controlled multi-sport event ever," said Bach.

"We've taken a big step forward. There has been a lot of movement forward in the battle against doping."

It is not only an increase in doping checks, up to 4,500 in Beijing from 3,600 in Athens, but also more sophisticated testing, stiffer punishments and the special attention competitors will get for any conspicuous behaviour.

"The developments are continuing and you can see changes in products and substances being used. We've reacted to that," said Bach, 54.

"If there are any positive tests it will show the system is working."

GOLD MEDAL

Bach, a trained lawyer who won a fencing gold medal for West Germany at the 1976 Olympics, added Germany and other countries had vowed to exclude anyone violating anti-doping rules from their next Games teams.

Possession of a prohibited substance constitutes a violation of the rules and athletes can now be tested more than once a day, he said.

In Germany, Olympians are required to sign anti-doping pledges and face stiff financial penalties for infringements.

"The overwhelming majority of the athletes are clean," Bach said. "The aim is to ensure they can have full confidence in an authentic competition."

Bach's cheery optimism on doping contrasted with his concerns about air pollution.

Beijing is one of the world's most polluted cities and becoming one of the most congested, causing concern to many athletes.

"The air pollution remains a problem," Bach said, adding the smog had been "especially bad recently. The existing conditions now are not what we would wish for looking ahead to August 8".

He added: "Quite a bit still needs to be done. The traffic volume is supposed to be cut in half, factories in the neighbouring provinces are supposed to be closed. That should happen as soon as possible."