JOHN LEICESTER,AP Sports Columnist, PARIS / With Queen’s rock anthem “Bicycle Race” blaring from loudspeakers, the Tour de France sets off for another day, the riders a blaze of color in their lurid shirts. This, undoubtedly, is one of sport’s most spectacular sights.

But is it believable?

A decade ago, when Lance Armstrong won the first of his record seven Tour titles, the answer to that question was largely “no.”

In this AP Photo Linus Gerdemann of Germany, center, is escorted by an official of the International Cycling Union, right, to the anti-doping truck after the second stage of the Tour de France cycling race over 187 kilometers (116 miles) with start in Monaco and finish in Brignolles, southern France, Sunday July 5, 2009. (Eds note: this was a standard anti-doping testing after each stage of the Tour. )

Doping had rotted cycling to the core. At least 80 percent of riders in the grand tours of France, Spain and Italy were doping, anti-doping scientists in Switzerland now calculate using blood tests from that time. Back then, researchers in Paris who were working on a method to catch one of the most common forms of cheating struggled to find clean samples to try out their new test.

“I had real trouble finding a negative,” says Francoise Lasne, the doctor at France’s anti-doping agency who conducted that groundbreaking research. “I thought the test wasn’t working.”

Now, in Armstrong’s comeback year, cycling can honestly claim that things are changing, that the dirt is not caked so thick.

Whether Armstrong was among those who doped in the past has never been adequately proved. He insists not. And it appears the Tour peloton he has returned to is cleaner than it has been for a long, long time.

Pristine? No.

But perhaps somewhat more believable.

The change can be seen, literally, in riders’ blood. A costly state-of-the-art blood monitoring program started last year is making the illicit use of performance-enhancing transfusions and blood-boosters such as EPO riskier and harder. Only those riders enrolled in the “biological passport” anti-doping program are allowed at the Tour.

It uses computer software and a panel of recognized experts from Europe and Australia to scrutinize riders’ blood-test results, looking for the abnormal variations that doping causes. A few years ago, when transfusions and EPO use were rife, riders’ readings were often all over the dial. That is less the case now.

“The vast majority of the peloton has very normal blood values,” says Anne Gripper, anti-doping manager for cycling’s governing body, the UCI.

That likely means two things — that the new anti-doping program is deterring riders from blood doping but that others have found ways to slip under its radar.

Micro-doses of EPO, if timed right, still might not be showing up — although they might be so small now that they aren’t giving cheats much of a performance kick, either.

Same goes for smaller transfusions. One pint of a rider’s blood transfused when the Tour heads into the Pyrenees this week or the Alps after that might not show up clearly enough for the UCI to be able to say definitely that cheating occurred and initiate disciplinary proceedings. Larger transfusions might.

Experts agree the biological passport represents a large and significant step forward for cycling. It is the first sport to seek bans using this technology. Riders whose blood readings appear suspicious but not sufficiently so to be actionable are also being targeted for follow-up testing that may help trip them up.

But no one is naive enough to believe that the program has fully closed the net on the smartest cheats or those who can afford the help of crooked doctors.

“It’s clear that riders have learned to dope within the passport,” says Michael Ashenden, one of the nine experts the UCI uses to analyze riders’ blood.

Correctly manipulating transfusions and mini-doses of EPO requires a certain amount of know-how but not a PhD.

“I could write it down on a post-it note,” Ashenden says.

Nevertheless, the passport is better than anything else science currently offers, and the deterrent factor does appear to be considerable.

One of the most encouraging signs is that some riders are starting to volunteer tips to drug testers about rivals they suspect are still cheating, breaking the code of silence that long prevailed in cycling, says an official directly involved with testing at this year’s Tour, which will roll into Paris on July 26.

Because of the necessary secrecy around drug testing, the official spoke on condition of anonymity. He believes that lesser-paid riders can no longer afford doping programs that are sophisticated enough to evade the passport regime and so are spilling the beans on those they suspect still can.

That is a somewhat cynical view. Riders also might be volunteering information for the simple reason that they have grown sick of cheating in their midst.

Either way, the evidence suggests cycling’s long-tarnished image is due a degree of rehabilitation and that those fans along the Tour route who shout “all dopers” — are wrong.

With the UCI, teams, riders and race organizers together forking out $4.2 million a year on the passport program, cycling at least deserves credit for owning up to its doping habit and trying hard to wean itself.

That is more than can be said for some other sports.