One year ago, after 83 tortuous hours over nearly 2,200 miles, cycling superstar and cancer survivor Lance Armstrong rode into the history books, becoming the second cyclist to win the Tour de France five consecutive times.

But it was not an easy win, as even Armstrong admits, and it came after one of his most uneven performances to date. There were two crashes and a dangerous near miss, and Armstrong conceded later, "I was not on top of my game."

Armstrong said at the time that ragged performance was due to overconfidence. "It was a complicated year, professionally, personally, emotionally," Armstrong said, in a news conference in Brussels last December. "It was a challenging year. I came into a point where I thought I was a little bit too comfortable with success. It's the hardest sporting event in the world and I took it for granted, and it's just not that easy."

This year, Armstrong attempts what no man has yet accomplished -- a sixth consecutive Tour de France win. Only he and Spaniard Miguel Indurain (1991-95) have won five straight. The obstacles against Armstrong this Tour are formidable.

"It's not a one-day race," Armstrong said this week at a news conference in Liege, Belgium, site of Saturday's prologue. "It's very difficult to win. There's many, many things that could happen. I could just flat out lose the race to a better rider. So I prefer to face it one day at a time."

His opponents in 2003 glimpsed something Armstrong has rarely allowed rivals to see: vulnerability. And this time, he is battling age -- he is 32, just past the age when even the Tour's past greats have tried for just one more, and fallen short.

And where last year Armstrong had help from the unexpected bad fortune of his chief competitors -- Jan Ullrich's famous spill in the penultimate stage in Nantes, Tyler Hamilton's broken collarbone -- this time around his rivals seem primed and ready for a chance to dethrone him.

"It's important that someone finally shows Lance that there's someone better," said Ullrich, the German captain of the T-Mobile team. The 1997 Tour winner, Ulrich is the rider Armstrong professes to worry about most. Speaking to reporters in Bonn recently, Ullrich, referring to his string of second-place finishes to Armstrong, said, "I don't want to be second, I want to be first."

Another cyclist with his sights on toppling Armstrong this year is the Spanish Basque rider Iban Mayo, who is coming off a win in June's eight-day Dauphine Libere, often seen as a precursor to the Tour. Armstrong won the Dauphine last year, but this year managed only fourth, a full two minutes behind Mayo. "It was an interesting week," Armstrong said after the Dauphine. "I was not as super as I would have wished."

Then there is Hamilton, Armstrong's once-loyal lieutenant and friend, who even has a home near Armstrong's in the northern Spanish town of Girona. Hamilton, also an American, put in a tough 2003 performance after breaking a collarbone early in the race, even managing to win a stage and, remarkably considering his injury, coming in fourth overall. At 33, Hamilton appears to recognize that this may be his last chance to win the Tour.

To age, and a stable of determined riders, add in the heavy weight of history. Three five-time winners have tried and failed to win a sixth Tour. If Armstrong should accomplish it, his status as cycling legend would be cemented.

Legend "is a big, big word and I'm not sure that I'm ready to talk about that right now," Armstrong said.

The route of this year's Tour appears to present a formidable obstacle. In an effort to maintain suspense and generate excitement, the organizers have devised a grueling counter-clockwise Tour around the country that leaves the most difficult mountain stages to the final week. After a relatively easy and mostly flat meander, the Tour will enter the Pyrenees on July 16 and 17, and then move into the unforgiving Alps on July 20. The next day will see an unprecedented uphill time trial to the infamous Alpe d'Huez, followed by two more days in the mountains. The penultimate stage, July 24, will be an individual time trial that could well decide the race.

Armstrong has called that final week of the Tour "Hell Week."

Weighed against those daunting odds is the fact that, "personally, emotionally," as he himself put it, Armstrong seems this year in a much better place. He began the year not knowing who would sponsor his team, with his contract with U.S. Postal Service set to expire in 2004. He found a new sponsor in Silver Spring-based Discovery Channel, which will have a small logo affixed to his U.S. Postal jersey this year, and take full sponsorship in 2005, when the team name will become Discovery Channel Cycling Team.

His personal life appears to have improved, after his announced divorce last year from his wife of five years, Kristen, and his now-public relationship with the singer Sheryl Crow. "Happier than I've ever been," is how he summed up his life in December, just before going public with Crow at a Hollywood movie premiere.

But among the distractions dogging Armstrong this year is a return of the doping allegations, unproven, which have trailed him since his miraculous comeback after testicular cancer six years ago. This time, the allegations have been raised in a new book, "L.A. Confidential: The Secrets of Lance Armstrong," written by David Walsh, a respected sportswriter for London's Sunday Times, with a French collaborator, Pierre Ballester.

The book -- which Walsh conceded in a published interview is based on "circumstantial evidence" -- largely bases its allegations on interviews with a former Armstrong aide, Emma O'Reilly, who says in 1998 and '99, Armstrong asked her to dispose of syringes for him, and then asked her to apply makeup to cover up needle marks. The allegations seemed to carry additional weight because O'Reilly still speaks favorably of Armstrong.

Armstrong launched a furious assault against the book. "I absolutely confirm we don't use doping products," he said at the news conference announcing the Discovery Channel sponsorship. Armstrong also took the unusual step of suing in London's High Court for damages and an injunction against Walsh, and asking a Paris court to force the French publisher to include Armstrong's rebuttal in the text.

"In the past, I've always let these type of allegations pass," Armstrong said, "but we can't tolerate it anymore. Enough is enough."

His attorney in the French case, Christian Charriere-Bournazel, argued in court that the authors were guilty of "dumping a load of garbage" on Armstrong just weeks before Saturday's start of the Tour.

The attorneys were not persuasive enough; the Paris court threw out the case, with the judge calling it "an abuse" of the legal system. In the end, it was Armstrong who was ordered to pay a token amount of one euro in damages.

"It's very difficult to win," Lance Armstrong said of world's premier cycling event. Three 5-time Tour de France winners have tried and failed to win a sixth."It's important that someone finally shows Lance that there's someone better," said Jan Ullrich, above. Armstrong considers Ullrich his top rival.