PARIS - Lance Armstrong hopes to do what no other cyclist has done, a test so demanding it has blocked the four great champions before him.

He wants to become the first six-time winner of the Tour de France, a punishing ride of 2,126 miles over countryside and mountains, three weeks of pain and sweat that burn the lungs and torment the legs.

Armstrong has won cycling's premier event the last five years, the first of his titles coming when he roared back from cancer. Now, at 32, he gets to see if the competitive fire still burns.

The race begins its great loop Saturday in Liege, Belgium, the latest chapter in what has become one of the biggest rivalries in international sports: Armstrong vs. Jan Ullrich, the German who risks forever carrying the label as perpetual runner-up to the Texan.

Armstrong is trying to overtake the five-time Tour de France winners: Jacques Anquetil, Eddy Merckx, Bernard Hinault and Miguel Indurain.

Ullrich has a different agenda. He has yet to fulfill the promise he showed in 1997 when at 23 he won the Tour on his second attempt. He has been a Tour de France runner-up five times. One more such finish and he joins Joop Zoetemelk, a Dutchman who raced in the 1970s and '80s, as the only riders to place second six times.

Ullrich was second to Armstrong in 2000, 2001 and 2003 and to Bjarne Riis in 1996 and Marco Pantani in 1998. Last year marked the closest duel between Armstrong and Ullrich. Armstrong was not assured victory until Ullrich skidded and crashed in the next-to-last stage, a rain-soaked time trial.

''This is my neighborhood, and nobody else is winning this race,'' Armstrong told himself in taking the key stage last year, a Pyrenean climb where he fell, got back up, screamed and stormed to victory in a rush of anger and adrenaline.

Predicting how Armstrong or Ullrich will fare in a trek as grueling and unpredictable as the Tour de France is uncertain science. Only as last year's race unfolded did it become clear that Armstrong, who won the warmup Dauphine Libere event, was struggling.

Ullrich, meanwhile, was coming back from injury and a ban for using recreational drugs and riding with a team rescued from financial peril. Yet he almost pulled it off - losing to Armstrong by just 61 seconds.

Armstrong must again ignore distractions, no easy task for a millionaire celebrity who counts President Bush among his friends and has taken up with singer Sheryl Crow since divorcing his wife, Kristin, after last year's Tour.

He is shadowed by a new book, ''L.A. Confidential, The Secrets of Lance Armstrong,'' that insinuates he probably has used drugs. The French-language book by journalists Pierre Ballester and David Walsh hit stores less than three weeks before the start of the race.

Armstrong has faced such accusations before - not least from Tour fans shouting along the route - and responded with lawsuits and an umpteenth denial.

''We don't use doping products,'' he said at news conference June 15.

''We're sick and tired of these allegations and we're going to do everything we can to fight them,'' he added. ''They're absolutely untrue.''

Armstrong also has a weight off his mind now that the Discovery Channel has agreed to a three-year, multimillion-dollar deal to replace U.S. Postal Service as the team sponsor next year. Instead of contemplating retirement, Armstrong plans to ride next year's Tour and possibly beyond.

''This is my job, to race and to win the Tour,'' he told cyclingnews.com. ''And the day that I don't show up worried about the competition, about myself, about my team, about the equipment, about the budget, about the sponsors, that's the day I have to go home.''

In the flat, fast first half of the counterclockwise race, he will look to his eight teammates for protection. Called ''domestiques'' in French because such riders labor like servants for their leader, they devote themselves to taming the flock of nearly 200 racers, shielding Armstrong from crashes, wind and challengers.

The crunch with Ullrich, or others, most likely will come in the last eight days over mountain stages and time trials. There, in cycling's version of man-to-man combat, Armstrong is at his best. Such riding allows him to sip champagne in the final ride to the finish on Paris' Champs-Elysees.

In addition to Ullrich, two riders bear watching: Iban Mayo of Spain, who won this year's Dauphine Libere in which Armstrong was fourth; and Tyler Hamilton of the United States, Armstrong's former teammate who finished fourth last year despite riding most of the way with a broken collarbone from a 35-rider pileup in the first stage.

Ullrich sustained a setback three weeks before this year's Tour, losing teammate Alexandre Vinokourov to injury. Vinokourov, a powerful climber who placed third last year, and Ullrich would have made a fearsome pairing.

Ullrich, however, is hungry.

''Standing on top of the podium in yellow whets my appetite for more,'' he said after winning the recent Tour de Suisse by one second. ''I'm taking this victory as motivation for the Tour.''