Rain on the Buckhead circuit for the men's and women's races could turn the outcome into a lottery, according to Britain's Chris Boardman, among the favorites.

"Because of the oil covering the roads in town, rain will make it extremely treacherous," was his prediction after a test run.

He has bitter memories of crashing on a rain-slicked road in the Tour de France, which wiped out his 1995 season.

Atlanta's capricious climate could mean that some race on dry roads in the 52-kilometer solo test while others, with narrow tires fully inflated for high-speed racing, may crash if conditions deteriorate.

The fear of changeable weather is heightened by the decision to send off the 40-strong field in groups of 10 with about one minute separating each rider. There will be almost an hour's gap between the departure of the 10th man and the first of the following bunch.

Spain took gold and silver in last year's world championships--Abraham Olano headed Miguel Indurain, whose five Tour de France wins were founded on his time-trial expertise.

"The time trial remains my prime target," said Indurain who finished nearly three minutes behind Swiss winner Pascal Richard in Wednesday's road race. "That course did not suit me, but it was good training for Saturday."

The field bristles with medal possibilities. Switzerland has two chances with Tony Rominger and Alex Zulle. Russia, too, is stocked with talent, namely Eugeni Berzin and Pavel Tonkov.

Bjarne Riis, the first Danish winner of the Tour, also has medal credentials.

Jeannie Longo of France goes for an Olympic double in the women's 26-kilometer timed test over two laps of the men's course.

After winning the road race on July 21, she left for Colorado to train at altitude. Last year, she captured the road race and time trial golds in the world championships.

One challenger, world pursuit champion Rebecca Twigg, has gone home because of problems with U.S. cycling officials. She been replaced by Jeanne Golay.

If any of the 24 riders is to challenge the dominant Longo it could be her teammate Marion Clignet, silver medalist in the track pursuit last week.

This story written by Reuters correspondents