By Nick Mulvenney

BEIJING, Feb 4 (Reuters) - Marathon world record holder Haile Gebrselassie will decide in the next two months whether to run in the endurance event at this year's Olympics despite fears that Beijing's air pollution will damage his health.

The 34-year-old Ethiopian will, however, definitely take part in his fourth Olympics in August, even if it is in the shorter track event that has won him two Olympic and four world titles earlier in his career.

"I'm going to run either the marathon or the 10,000 metres," Gebrselassie, who suffers from respiratory problems, told Reuters on Monday. "I do want to come here to compete in the Beijing Olympics. It depends on just the temperature and the pollution, especially the pollution.

"In a marathon, we run for more than two hours. I don't want to discourage other athletes but I've got to think about myself because I have a health problem.

"I'm thinking about here in Beijing, whether it will be ok or not ... (I'll decide) in two month's time."

Pollution is one of the biggest problems facing Beijing in the run-up to the Games and Olympic chief Jacques Rogge said last year that events like the marathon might have to be rescheduled if contingency measures did not have the desired effect.

Gebrselassie said fast times in the marathon in Beijing, where 30 degree Celsius temperatures and high humidity are the norm in August, would be "impossible" and scoffed at the suggestion that the race might be run in the middle of the day.

"Forget that, if they are going to run it in the middle of the day, that's just killing the athletes," he said.

"It should be in the early in the morning, at 6.30 at the latest."

(Editing by Greg Stutchbury)