BAGHDAD, Iraq - Less than 24 hours before Saddam Hussein returned to court on charges of crimes against humanity, the police in northern Iraq said Sunday that they had arrested 10 Sunni Arab men carrying orders from a fugitive associate of Mr. Hussein's to assassinate the court's best-known judge.

Iraqis in Najaf held photos of relatives they said had been killed by the government of Saddam Hussein.

Prosecutors have said they plan to bring their first witnesses against Mr. Hussein and other defendants as the court resumed in Baghdad on Monday after a six-week recess.

Defense lawyers say they will demand a new 45-day adjournment while the court considers motions to annul the proceedings on the ground that the American role in creating the court, formally known as the Iraqi High Tribunal, has voided its authority under Iraqi and international law.

The police commander in the northern oil city of Kirkuk, Gen. Sarhad Qader, said the 10 men seized there in two predawn raids on insurgent safe houses on Sunday were being questioned in connection with a bomb plot to kill Raid Juhi, the chief investigative judge of the court that is trying Mr. Hussein.

General Qader said the men were caught with a document containing orders to carry out the killing from Izzat Ibrahim al-Douri, Mr. Hussein's former vice president and the last of his inner circle of associates to have evaded capture or death.

The allegation against Mr. Ibrahim came two weeks after an apparently false report that he had died appeared on a Web site operated by loyalists of Mr. Hussein's banned Baath Party. The American military command said it was treating the report as disinformation, and even the Baath Web site later withdrew it.

American commanders have identified Mr. Ibrahim, 63, as perhaps the major leader of the insurgency's Baathist wing, and an architect of the alliance it has struck with Islamic militants who have carried out many of the war's bloodiest attacks.

As American and Iraqi officials went through security drills at the courthouse for the trial in the heavily protected complex known as the Green Zone, officials in Ottawa and London confirmed that four Western aid workers - an American, a Briton and two Canadians - were kidnapped in Baghdad on Saturday. They gave no details, and the American Embassy here issued a statement saying, "We are aware of the reports that an American national has gone missing and are investigating it as a matter of urgency."

In London, officials identified the missing Briton as Norman Kember, 70, and said he was a retired professor of a London medical college.

Insurgents have made a major tactic of kidnapping foreign civilians and have seized at least 200 in the 31 months of the war, dozens of whom have been killed, some by beheading. But the tactic has been used much less frequently since American and Iraqi troops overran the insurgent stronghold of Falluja outside Baghdad last November, uncovering bunkers where some of the hostages had been held. Since then, foreigners, like Iraqis, have faced a greater threat from suicide bombings.

The arrests in Kirkuk of the men alleged to have been plotting to kill one of the Hussein prosecution judges added a new element of tension to the protracted process involved in bringing Mr. Hussein to trial for the repression during his 24 years in power, which prosecutors have said resulted in two million deaths. The trial is one of as many as a dozen that prosecutors plan for the ousted ruler and his associates. Nine people directly linked to the process have been killed, including two defense lawyers in the past six weeks.

Mr. Juhi is not among the five judges presiding at the trial that resumes on Monday, in which Mr. Hussein and seven others are charged with the torture and killing of 148 men and teenage boys from the town of Dujail, north of Baghdad, after an assassination attempt against Mr. Hussein in 1982. But as the judge who has led the tribunal's investigations, appearing frequently on television confronting Mr. Hussein in pretrial hearings, he has been the most visible of the Iraqis directly involved in the cases against him.

Mr. Juhi, 35, has spoken of several plots to kill him since he became a household name in Iraq with his unflinching and occasionally scolding attitude toward Mr. Hussein at the former ruler's first court appearance, a hearing at an American military base on Baghdad's outskirts in July 2004. On that occasion, and again at the trial's opening last month, Mr. Hussein adopted a defiant posture, saying he would not recognize the court's authority.

General Qader, the Kirkuk police commander, said the raids that uncovered the plot to kill Mr. Juhi had also found three car bombs ready to be driven to targets, as well as other documents linking the men seized in the raids to Abu Musab al-Zarqawi, the leader of Al Qaeda in Mesopotamia, and to Ayman al-Zawahiri, the deputy to Osama bin Laden. He said the document ordering Mr. Juhi's assassination was signed with a pseudonym, "Sheik of the Mujahedeen," and that the captured men, one of them a former secret police officer under Mr. Hussein, had said that that was the title used by Mr. Ibrahim.

Violence against those involved with the tribunal has become a coda, most recently with the shooting deaths of 2 of the 13 defense lawyers who appeared in court for the first session. The seven others killed in connection with the tribunal have included one of its team of about 25 trial and investigative judges, shot in his driveway with his son earlier this year; the brother of the chief prosecutor, Jaafar al-Mousawi; and three other court officials. At least a dozen others working at the tribunal have quit after death threats.

The viability of continuing with the trial came into question when the Iraqi Bar Association declared a boycott after the killing of the defense lawyers and demanded that the trial be moved abroad. But after talks led by American officials, important members of the defense team, including Khalil al-Dulaimi, the lead lawyer for Mr. Hussein, said they had accepted protection from Iraq's Interior Ministry, and would be in court on Monday. American officials have said they are confident that each defendant will be represented by at least one lawyer.

Mr. Dulaimi has said the defense strategy will be to challenge the tribunal's legitimacy. Others on the defense team have said a crucial argument will be that the tribunal, originally founded under an American occupation decree and adopted into Iraqi law only last month by the transitional parliament, contravenes a provision in the Geneva Conventions that the lawyers contend forbids occupying powers from creating judicial institutions.

To bolster the challenge, Mr. Hussein's defense team hoped to be joined in court on Monday by Ramsey Clark, the former American attorney general, who has a long and controversial history of offering legal advice to toppled foreign leaders, including the former Yugoslav president, Slobodan Milosevic. Mr. Clark, 77, arrived in Baghdad on Sunday.

But an American government official said Sunday night that Mr. Dulaimi, Mr. Hussein's lawyer, had failed to submit the paperwork necessary for Mr. Clark to qualify for the court under Iraqi rules that permit foreign lawyers to participate in trials as associates of Iraqi lawyers. The official said Mr. Dulaimi "has been invited to do so and told how to do so on a number of occasions" and had not responded, with the effect that Mr. Clark would not be admitted to the court, at least on Monday.

Mr. Clark flew from Amman, the Jordanian capital, with Najeeb al-Nauimi, a former justice minister of Qatar, one of the dozens of other foreign lawyers sympathetic to Mr. Hussein's legal rights who have been recruited to his cause by Raghad Hussein, Mr. Hussein's oldest daughter, from her self-exile in Jordan.

Mr. Clark, who served as attorney general under President Lyndon B. Johnson, summarized the arguments he said the defense team planned to make in court. "A fair trial in this case is absolutely imperative for historical truth," he told Reuters. "A court cannot be a court unless it is absolutely independent of all external pressures and forces."

Tensions over the trial have been evident recently in a series of protests in Baghdad, and in the Shiite holy cities of Karbala and Najaf, at which crowds of several hundred, mostly Shiites, have burned Mr. Hussein in effigy, hoisted signs saying "No, no to the devil!" and demanded that he be hanged after a quick trial.

Annotazioni − An Iraqi staff member of The New York Times contributed reporting from Kirkuk for this article.