The trial of maverick presidential candidate Ayman Nour opened chaotically in a small south Cairo courtroom Tuesday with the defendant pleading not guilty to charges of forging official documents, and supporters noisily declaring that the case is a sham.

"The goal of all this is to smear my campaign," Nour said as he sat in a metal mesh enclosure used in Egyptian courts to contain defendants. "I will carry on my campaign . . . even if it's from this cage."

Protesters rushed the courtroom and chanted inside. Hundreds of riot policemen stood guard at the courthouse entrance and dozens more took up positions inside. No one could remember such tumult at an Egyptian trial.

Nour is the only declared opposition candidate who has been actively campaigning to unseat President Hosni Mubarak in a vote this fall. Nour has been charged with forging hundreds of petitions that were filed to legalize his Tomorrow Party, which gained official status last fall.

The Bush administration has been pressing Mubarak to ensure a fair election and to permit freedom of assembly, association and access to the media for Egypt's myriad political factions. Mubarak has billed the balloting as Egypt's first ever multi-candidate presidential vote.

Opposition leaders regard the rules for who can run as restrictive and many of them say Mubarak should not be allowed to run.

Political protests have become common in Cairo during the past few months, with an increasing number of participants. Organizers include a variety of political and nongovernmental groups under the label Kifaya, or Enough. The Muslim Brotherhood, which Egyptians widely regard as the largest and best-organized opposition group, has also taken to the streets. On Tuesday, Brotherhood leaders called for joint demonstrations of all reform movements.

Police jailed Nour for six weeks last winter while the forgery case was under investigation. Secretary of State Condoleezza Rice canceled a visit to Cairo in response, but came to the capital last week and met with democracy activists, including Nour, who is free and who has been stumping for president.

The morning hearing got underway in confusion and occasional jostling. When Nour arrived, he said he was being barred from the courtroom. Supporters and lawyers stormed the room and were pushed back by police. After some give-and-take, a court officer let Nour, some backers and some journalists into the steamy courtroom one by one. "This is a prison, not a courthouse," Nour said at one point.

He was joined in the courtroom cage by four other defendants who are, in effect, his accusers. Through a lawyer, they told the court that Nour ordered them to forge documents. Two other defendants were missing. Nour said he had never seen any of them before.

Attorneys for Nour -- several of them were present in the courtroom -- boisterously shouted objections. At one point, Judge Abdel Salam Gomaa stalked out of the room, saying, "Is it me who is running the session or is it you?" He returned 15 minutes later.

Chants of "Free Ayman Nour," "We Love You, Ayman" and "Scandal, scandal" filtered into the courtroom from the streets. Pro-Nour banners hung from nearby buildings and police barricades. One read, "A Million Ants Can Eat the Corpse of an Elephant," a reference to the belief of Tomorrow supporters that elections, if fair, would threaten Mubarak's 24-year rule.

One of Nour's attorneys, Amir Salem, said in an interview that the trial keeps Nour from campaigning effectively because he is subject to being called to attend hearings. If convicted, he would be barred not only from running for president, but from subsequent parliamentary elections, also scheduled for this autumn.

The next hearing is set for Thursday. Nour's attorneys are asking that several government ministers be called to testify, including officials who originally approved the legalization of the Tomorrow Party.

Presidential candidate Ayman Nour flashes a victory sign at a court in Cairo. He pleaded not guilty to forgery charges.