An American student charged in an al Qaeda plot to kill President Bush said his Saudi captors whipped him on the back, punched him in the stomach and kicked him, according to a doctor who examined the student and testified yesterday before the judge who must decide if the student was tortured.

Ahmed Omar Abu Ali also said he was shackled with his arms above his head for more than seven hours after initially refusing to cooperate with FBI agents who traveled to Saudi Arabia to interrogate him in 2003, according to the doctor, Allen Keller. Keller, who is program director of the Bellevue/NYU Program for Survivors of Torture in New York, examined Abu Ali in April at the request of his attorneys.

"He told me it was excruciatingly painful,'' Keller testified at a hearing in U.S. District Court in Alexandria. He said he believes the alleged mistreatment constituted torture and cited as evidence scars consistent with whipping that he said he observed on Abu Ali's back.

The testimony means that a judge will have to evaluate the opinions of clashing experts on a key issue in the high-profile case. Attorneys for Abu Ali, 24, of Falls Church say that he was tortured in Saudi custody and that statements that form the crux of the government's case should be thrown out because they were obtained under duress.

The hearing, which started last week and runs through tomorrow, is to determine whether Abu Ali's statements to Saudi interrogators will be admitted into evidence.

Prosecutors deny that Abu Ali was tortured, and they sought to discredit Keller's testimony yesterday by questioning his objectivity and saying he has a tendency to always believe people who say they were tortured. Asked by Assistant U.S. Attorney David Laufman how many alleged torture victims he has examined, Keller said about 500.

"How many of those 500 or so did you find to be malingering?'' Laufman asked.

"Very few,'' Keller replied.

Prosecutors presented their own expert earlier yesterday, Robert Katz, a dermatologist. He testified that four marks he saw on a photo of Abu Ali's back were unlikely to have been caused by whipping. "They show no evidence of scarring,'' said Katz, an expert on skin trauma. "They are limited to the upper back.''

On Monday, a U.S. government doctor who examined Abu Ali in February, when he was flown back from Saudi Arabia to face terrorism charges, testified that he could not conclude that the marks on Abu Ali's back came from physical abuse. He said they could also be the result of old scarring or could have been self-inflicted.

Abu Ali is charged with conspiracy to assassinate President Bush and other terrorism counts in connection with the alleged al Qaeda plot, which prosecutors say also envisioned a Sept. 11-style attack in the United States. Prosecutors say that Abu Ali has admitted his participation and that he planned to shoot the president or blow him up with a car bomb. He admitted that the plan never got past the idea stage, prosecutors have said in court papers.

It is unclear when U.S. District Judge Gerald Bruce Lee will rule on the torture question. The case is scheduled to go to trial next week.