An unusual mixture of nerves and excitement fills Lance Armstrong on the eve of his return to professional cycling at the Tour Down Under in Australia.

The seven-times Tour De France winner insists he has no real chance of winning the six-day race after spending the last three and a half years "drinking beer and sitting on (his) ass", but he has no regrets about his decision.

"I wouldn't want to sound like a slacker but I have no major goals other than to make it through and get back into the rhythm of racing," he told a packed news conference in Adelaide on Saturday.

"I'm extremely motived and extremely uncertain about how it will go. The main thing is just to stay out of trouble, try to stay up front and avoid the drama." Armstrong quit professional cycling after winning the 2005 Tour de France but announced late last year he was making a comeback at age 37.

The Texan said he partly missed the thrill of competition but was driven by a greater cause, to help promote cancer awareness.

Painted on his new bike are two numbers -- 1,274 and 27.5. The first represents the number of days since his last race in 2005, the second represents the people who have died from cancer in that period.

"That's the number in millions, it means 27.5 million," Armstrong explained.

"It seems like I've been off the bike for a long time but it's only been three and a half years, but in the meantime 27.5 million people have died from cancer.

"That's a staggering number but that's why I'm here, I wanted to take a really strong message around the world, to talk about the global burden of this disease."

'LIVE STRONG'

Not everyone is pleased about Armstrong's comeback.

Accusations of doping have dogged him throughout his career but the American has never failed a test and has always maintained his innocence.

His decision to return at the Tour Down Under, a relatively smaller event that was only recently added to the ProTour calendar, has created unprecedented interest in the race.

The American arrived under the sort of tight security normally reserved for heads of state and his pre-race news conference drew a throng of local and international media.

Looking relaxed in denim jeans and black t-shirt with "Live Strong" printed on the front, Armstrong said he was expecting a different reception in Europe later in the year.

"The attention has been more than I expected but I think that's good for cycling and it's good for the fight against cancer, it's good for all of the reasons I wanted to come back," he said.

"There's going to be moments when it's hot and cold and I know that and I'm more prepared to ride through the hot ones and the cold ones."

COMEBACK? SERIOUSLY?

Armstrong will make his official comeback at Sunday's 51 kilometre criterium around the city streets of Adelaide, riding for the Astana team. The six-day, 800km tour starts on Tuesday.

Astana team boss Johan Bruyneel thought Armstrong was joking when he received a call from him last year to say he wanted to make a comeback.

"After three or four conversations I could feel it was starting to be serious, so I went over there (to Texas) and after I came back there was no doubt in my mind that he was very serious and it was going to happen.

"His training so far has been very good, in fact he is ahead of where he was when he was racing before for this time of the year. I have no doubt he will get back to the levels he was at before."

While conceding his chance of winning his first race were minimal, Armstrong said it did not mean he did not want to win or would not be trying his best.

"I don't have any clear ambitions or standards in my mind as to what's a success. To me, it's partly successful just being here and being able to race earlier than I would have," he said.

"But if the opportunity is there, I will certainly take it. I guarantee you I will take every opportunity to be at the front of the race and be active.

"There's not a doubt, no bluffing, no hiding. If the race dictates that and I feel good I promise you I will attack but I just don't know that I will be in a position to do that."