An American student charged in an al Qaeda plot to kill President Bush and conduct a Sept. 11-style terrorist attack in the United States may face additional charges in the next several weeks, federal prosecutors said yesterday.

Prosecutors revealed the possibility of upgraded charges at a hearing in U.S. District Court in Alexandria in the case against Ahmed Omar Abu Ali. They did not disclose what the new counts could be.

Abu Ali, 24, of Falls Church, is charged with material support of al Qaeda in a plot to kill Bush and establish an al Qaeda cell in this country. The government says he confessed to the assassination plot while being detained in Saudi Arabia and admitted discussing with al Qaeda his plans to conduct attacks in the United States that included crashing hijacked planes into buildings.

But defense attorneys contend that any statements Abu Ali made while in Saudi custody were obtained through torture. As the case moves toward trial in October, the torture allegation promises to be key in determining whether the high-profile case -- and other terrorism cases that involve a defendant's conditions of confinement in a foreign country -- can effectively be prosecuted in a U.S. courtroom.

If a federal judge concludes that Abu Ali was tortured, much of the evidence against him could be thrown out because it was obtained under duress.

Two doctors who examined Abu Ali found evidence that he was tortured in Saudi Arabia, including scars on his back consistent with having been whipped, defense lawyers have said in court papers.

But at yesterday's hearing, prosecutors repeated their denials that Abu Ali had been tortured, with Assistant U.S. Attorney David Laufman calling the allegation "a fabrication." When Abu Ali was questioned by FBI agents in Saudi Arabia in September 2003, Laufman said, he made "a cryptic reference to mental torture" but said nothing about physical mistreatment.

The torture allegations came up yesterday in arguments over other pretrial motions in the case. Those claims are likely to be a key part of a hearing starting Sept. 19 that could last up to three days.

Also yesterday, U.S. District Judge Gerald Bruce Lee said potentially important evidence cannot be turned over to the defense because none of Abu Ali's attorneys has obtained security clearance to review classified information. The government recently rejected the clearance application filed by one of the lawyers, Ashraf Nubani. It is unclear why. But Lee, who is overseeing the case, also said the amount of classified evidence is small.

Prosecutors unsealed a six-count indictment against Abu Ali on Feb. 22. At a detention hearing a week later, an FBI agent testified that Abu Ali had admitted that he and other members of an al Qaeda cell in Saudi Arabia planned to hijack airplanes overseas and crash them into targets in the United States.

The conspirators also discussed plans to kill members of Congress, blow up ships in U.S. ports and aircraft at U.S. military bases and free terrorist prisoners at Guantanamo Bay, Cuba, the agent testified. The charges came after Abu Ali's family mounted a highly public campaign for his release from Saudi custody. He was arrested by Saudi security officials in 2003 while studying at a university there.