PARIS — The 2009 Tour de France will feature a tough mountain stage on its penultimate day, a change in tradition that could complicate Lance Armstrong's possible return.

The route, aimed at keeping suspense going to the very end of the 106-year-old event, was unveiled Wednesday in Paris. Often, the Tour finishes with a time trial before what is largely a ceremonial ride on the final day.

The steep climb up the notorious Mont Ventoux could pose a particular challenge for Armstrong, who has never won on the rocky slopes of the fabled ascent in the south of France.

The seven-time Tour champion is making a comeback after three years of retirement, but it's still unclear whether he will race in the event.

The three-week Tour begins July 4 and will cover 2,141 miles with 20 major mountain climbs — slightly fewer than the average of 22-23 climbs in recent years.

Mont Ventoux will be the 20th of 21 stages. After 19 days of racing, the climb on which a British rider died in the 1960s promises to be a test for tired legs and minds, and possibly decisive in determining the winner.

"The Ventoux will blow things up," said Jean-Francois Pescheux, who helped design the route as director of competitions for ASO, the company that organizes the Tour.

From its start in the principality of Monaco, the Tour will go across flatlands of the Mediterranean coast to Barcelona, Spain, then head sharply uphill into the Pyrenees. The first Pyrenean stage, to the Arcalis mountain station, is also the longest of this year's Tour at 139 miles. The long ride and steep uphill finish should give the first indication of the favorites.

After two more trying days of ascents in the mountains that form the border between France and Spain, the Tour goes through central and eastern France before tackling the Alps. Three days of climbs in those mountains, including the Tour's high-point at 8,113 feet on the Grand Saint-Bernard pass, followed by a time trial should further separate the field.

Then comes the Mont Ventoux.

Organizers also have revived the team time trial, which had fallen out of favor in recent years. The highly technical discipline will be run on Day 4, but its relatively short distance of 23.6 miles should not be a major factor in the determining the favorites.

Armstrong initially said when he announced his comeback last month that he would aim for an eighth Tour victory, stunning the cycling world.

But a less-than-enthusiastic response from Tour organizers and renewed discussion in France of whether Armstrong used performance-enhancing substances — he insists he did not — are now reportedly giving him reason to reconsider. Armstrong has said that he will race the Giro d'Italia in May, but is sounding less certain of riding the Tour in July.

Tour director Christian Prudhomme again Wednesday offered only a guarded response to the prospect of Armstrong's return to the race, saying it would be "neither a good nor bad thing" for the Tour.

Pescheux expressed doubts that the 37-year-old cyclist, who won a record seven Tours from 1999-2005, could contend after three years away from cycling.

"I think he will rapidly realize that things are not the same," Pescheux said.

Pescheux added that Armstrong always managed to adapt to the yearly route changes of previous Tours, and he thinks the Texan would again if he chose to race in 2009.