For the second straight year, no rider is expected to dominate the Tour, in part because many of the cyclists who would have been expected to compete for the victory are not here.

Floyd Landis, who finished first last year, is awaiting the result of an arbitration hearing over his positive drug test in last year’s Tour. Ivan Basso, who finished third in 2004 and second in 2005 before being barred last year on suspicion of doping, acknowledged his involvement in a doping scheme this year and has been barred from racing for two years. Jan Ullrich, the winner in 1997 and the perennial runner-up to Lance Armstrong, retired after being barred from last year’s race on suspicion of doping.

Many of the riders who are here are bristling over being forced by cycling’s governing body to sign a statement guaranteeing that they will give up a year’s salary if they are caught using performance-enhancing substances. While few said they disagreed with the spirit of the statement, they complained that it was forced on them without their consultation.

Robbie McEwen, the Australian sprinter who rides for the Predictor-Lotto team, said he believed that most if not all of the riders agreed in principle with the antidoping pledge. He added, “But it needs to be further reaching, past just the riders themselves — to the team managers, the team doctors, the soigneurs,” or team assistants, who provide massage therapy and other general services to the riders.

While there have been promises of reform before, some riders expressed hope that the overwhelmingly negative atmosphere around their sport would begin to dissipate.

“Last year, the atmosphere was so difficult for us, and still things did not change,” Christophe Moreau, the top French rider and the recent winner of the Dauphiné Libéré, a major tuneup for the Tour de France, said at a prerace news conference.

“This year, things are changing,” Moreau said. “They need to change, for the sake of the teams, the sponsors and the Tour organization. We need to get the credibility of cycling back.”

That will not be easy. This week, the world’s leading sprinter, Alessandro Petacchi, who was expected to be a top contender for several stage victories in the race’s first week, was withdrawn from the race by his Italian team, Milram.

The withdrawal came after the Italian Olympic Committee recommended a one-year ban for Petacchi because a drug test in May, during the Giro d’Italia, showed he had in his system too much of an asthma medication that he had a doctor’s permission to use.

As a sprinter, Petacchi was not expected to compete for the overall victory in the race, which covers 2,218 miles over 21 days of racing, moving from Britain to Belgium and then in a clockwise tour around France to the finish in Paris.

But the race is to be considered a wide-open affair, with any one of nearly a dozen riders viewed as a possible winner. If anyone is considered the favorite, it is Alexander Vinokourov, a 33-year old Kazakh who rides for Astana. The team, named after the Kazakh capital, was put together by Vinokourov after he was unable to start last year’s race when several teammates on the Liberty Seguros team were barred for their involvement in the Operation Puerto doping scandal in Spain.

Vinokourov can be frighteningly aggressive, with slashing attacks that often go against the conventional wisdom of how to ride a race. But he, too, has faced doping suspicions after acknowledging last week that he had worked with Dr. Michele Ferrari, an Italian doctor who was found guilty of sporting fraud and malpractice in 2004 but who won an appeal two years later. Vinokourov said he consulted Ferrari for training purposes but not for medical advice.

Vinokourov’s top competitor could be on his own team: Andreas Klöden, 32, of Germany. Klöden finished third last year, behind Landis and Óscar Pereiro, and he won the Flèche Wallonne one-day race this year. While the team denied there was any friction between Klöden and Vinokourov, they have a history. In the 2005 Tour, Klöden and Ullrich, both riding for T-Mobile, chased down a breakaway that was being led by their teammate Vinokourov.