MALIBU, Calif. - A lab technician testified yesterday that she taped a do-not-cross line across the floor of her workspace to keep Floyd Landis' observers from interfering with tests of the Tour de France champion's urine samples.

Landis is accused of using banned synthetic testosterone during his Tour de France victory last year.

A three-man arbitration panel hearing nine days of testimony will decide whether to uphold Landis' positive doping test. If it does, he could face a two-year ban from cycling and become the first person in the 104-year history of the Tour whose title was stripped.

During the race, the Lancaster County native was tested eight times. One of those tests was positive.

The U.S. Anti-Doping Agency plans to bring three-time Tour winner Greg LeMond to the stand today. That figures to offer a much-anticipated break from the dry science and procedural bickering that have filled the first three days.

Cynthia Mongongu of the Chatenay-Malabry lab in France talked about her makeshift barricade and said she used it to keep two observers at bay.

She also talked about being "accosted" by an expert observing the testing of Landis' backup "B" samples.

"I needed to be able to concentrate on my work," she said.

Landis' attorneys raised the issue during cross-examination to try to puncture Mongongu's credibility and prove she was biased in the case.

They asked why she filed a sworn statement about interference from the Landis observers but not from J. Thomas Brenna, who was present to observe for the anti-doping agency.

"It wasn't necessarily Dr. Brenna," said Mongongu, an analytical chemist at the lab. "It's just the whole . . . any kind of group of people who are around me."

The attorneys followed those questions with more about whether Mongongu was the source of leaks to the French newspaper L'Equipe about any positive tests.

"Absolutely not," Mongongu said. She also denied knowing the source of the leaks.

Both sides have decried the number of leaks from the French lab. The Landis camp is trying to use them as part of a larger effort to show a pattern of incompetence, and possible malfeasance, at the lab, outside Paris.

Much of the testimony yesterday concerned the backup samples of Landis' seven negative tests. The backup samples were, at the anti-doping agency's request, subjected to carbon isotope ratio testing to look for synthetic testosterone.

Four of the seven returned "abnormal testosterone profiles," and the Landis camp is trying to prove that it was a result of mishandled tests.

Early in the cross-examination, Landis attorney Howard Jacobs grilled Mongongu on the number of times she had called for assistance. She said she couldn't remember the number of calls or what they were about.

But she had a better memory of some specifics of the testing, such as what she did with bottles from some of Landis' original tests last year.