PAU, France — Tour de France rider Alexandre Vinokourov tested positive for a banned blood transfusion after winning last weekend’s time trial, prompting his Astana team to pull out of the race yesterday and police to raid the team hotel.

Despite the latest heavy blow to a sport reeling from doping scandals, Tour de France organizers said the race would go on.

The Kazakh rider, a one-time favorite to win cycling’s premier event, was tested after his victory in the 13th stage time trial on Saturday.

“Vino has tested positive having to do with a blood transfusion and the team is leaving the Tour,” team spokeswoman Corinne Druey said, using the rider’s nickname.

Astana team manager Marc Biver said Vinokourov was sent home. His backup B-sample test results are expected by the end of the week.

“Alexandre denies having manipulated his blood,” Biver said, adding that the rider believes that “blood anomalies in his body” may have resulted from a crash he was involved in last week.

About 30 police officers, some in plain clothes, descended on Astana’s La Palmeraie hotel in Pau and sealed it off, preventing more members of the team from leaving.

The case brought back memories of some of cycling’s darkest days. In 1998, police raids turned up a stash of performance-enhancing drugs in a Festina team car, plunging the Tour in crisis.

Vinokourov, a pre-race favorite, also won Monday’s 15th stage. He was 23rd in the overall race standings. The Tour finishes in Paris on Sunday.

Race director Christian Prudhomme said the case showed that cycling’s drug-testing system doesn’t work.

“It’s an absolute failure of the system,” he said. “It is a system which does not defend the biggest race in the world. This is a system which can’t last.”

World Anti-Doping Agency chief Dick Pound, a frequent critic of cycling’s doping record, said the sport should have cleaned itself up by now.

“It’s almost impossible to be at the front of the pack these days without doping,” he said.

Once seen as a favorite to win the Tour, Vinokourov dropped out of contention for good Sunday after losing 28 minutes, 50 seconds to race leader Michael Rasmussen.

The French sports daily L’Equipe, which first reported the positive test on its Web site yesterday, said the analysis was conducted by the Chatenay-Malabry lab on the outskirts of Paris. It said two distinctive types of red blood cells were found in the A sample and showed that Vinokourov received a blood transfusion from a compatible donor shortly before the time trial.

A senior French anti-doping official confirmed to the Associated Press that there was a positive test for a blood transfusion taken from a rider at the Tour on Saturday. He said the test found two different types of blood, one from the rider, one from a donor.

The official spoke on condition of anonymity because no official announcement had been made.

The president of cycling’s world governing body, the UCI, said he could not comment as long as the result of the backup B-sample had not been confirmed.

“We have a process in place and we have to see this process through,” Pat McQuaid told the Associated Press in a telephone interview.

Tour de France officials expressed dismay at the latest doping case to scar the event and the sport as a whole.

“Everyone will feel betrayed,” said Patrice Clerc, head of Amaury Sports Organization, which owns the Tour. “The public wants to see a credible winner.”

But Clerc said it “never crossed my mind” to halt the Tour.

“We have started a war against doping,” he said. “It’s out of the question to give up.”

Vinokourov has been a crowd favorite along the course route this year. He was injured in a crash in the fifth stage, requiring stitches in both knees.

“With a guy of his stature and class, in cycling’s current situation, we might as well pack our bags and go home,” said British rider David Millar, who came back from a two-year doping ban in the Tour last year.