A Federal Court judge has struck down as “patently unreasonable” the government’s decision to deport a suspected terrorist who faced a significant risk of being tortured in an Egyptian jail.

Justice Eleanor Dawson said that since a federal immigration official was not allowed to see the secret dossier against Mohamed Mahjoub, he did not have the information on which to base a decision that could result in his mistreatment or torture.

The official had to decide whether Mr. Mahjoub’s threat to national security outweighed his risk of being tortured in Egypt. But in making that assessment, the official was not allowed to review the complete dossier prepared by the Canadian Security Intelligence Service, only a summary of it.

“Without that information,” Judge Dawson wrote, “the delegate could make no independent and proper assessment of the degree to which Mr. Mahjoub poses a threat to Canada’s security.”

Mr. Mahjoub, 44, of Toronto, is one of six terror suspects detained on security certificates that have been issued by cabinet ministers based on secret evidence. Five of the men are Arab; all contend they will be tortured if returned to the repressive regimes from which they fled.

CSIS alleges Mr. Mahjoub is a high-ranking member of an Egyptian terrorist group, Vanguards of Conquest.

In making her decision, which was released yesterday, Judge Dawson conceded that she avoided a critical question. “I acknowledge an issue of importance has been raised which I do not decide: whether circumstances would ever justify deportation to face torture.”

That question, she said, needs to be decided by a future security certificate case that has a more complete file of evidence. She suggested that there are “powerful” indications that deporting anyone to face torture would shock the Canadian conscience and violate fundamental justice.

In January, 2002, the Supreme Court ruled that terror suspects can be deported only in exceptional circumstances to countries where they face a substantial risk of torture. The Supreme Court did not define those circumstances. Rather, the court said the scope of the exception would be defined as individual cases moved through the justice system.

The case of Mr. Mahjoub, who admitted to working for Osama bin Laden’s agricultural company in Sudan, will now be returned to immigration bureaucrats, who must again decide whether his deportation can be justified in the face of his potential torture.

Mr. Mahjoub has been in custody since June 2000.

Judge Dawson’s ruling represents a significant setback for the federal government as it seeks to deport foreign-born terrorist suspects, including Mohamed Harkat of Ottawa.

If it stands unchallenged, the Federal Court decision will raise the bar for such deportations.

Judge Dawson said federal officials must carefully examine evidence that an individual poses a danger to Canadian security “and weigh the factors which go to the reliability of that information,” including the motivation and track record of CSIS informants.

She said federal officials also must consider whether a terror suspect’s detention has reduced his threat level.

“It may be, for example,” the judge said, “that the fact of apprehension and disclosure of a person’s associations or activities will neutralize their future ability to conduct clandestine activity.”

One of Mr. Mahjoub’s lawyers, John Norris, said the decision represents the first time a judge has grappled with the notion of what the Supreme Court meant by “exceptional circumstances.”

It’s a legal exercise that needs to take place, he said, because the federal government now believes it has “as an open invitation to send people to torture, if it is so inclined.”

The federal government has tried to deport Mr. Mahjoub and Egyptian Mahmoud Jaballah even though its own officials concede the men face a substantial risk of torture if removed.

Mr. Harkat’s wife, Sophie, said the Mahjoub case raises the question of how long the government is prepared to incarcerate terror suspects without formal charges or trials.

“How long are they going to keep them in there?” Sophie Harkat asked yesterday. “I think they have to put them under strict bail conditions, with security bracelets and restrictions about their movements and phone calls, but let them back with their families. . . They can’t hold people forever.”

Public Safety Minister Anne McLellan said she hadn’t seen the judgment yet, and couldn’t comment specifically on the findings. However, she defended the security certificate process in general. “These people, by definition, because of the process they’re involved in, we have made a determination . . . that they are a threat to security, so we will take whatever steps are necessary to ensure they don’t endanger the security of Canadians,” Ms. McLellan said.

CSIS contends that Mr. Mahjoub was a high-ranking member of Vanguards of the Conquest, a radical wing of the Egyptian Islamic Jihad. That group merged with al-Qaeda in 1998.

Islamic Jihad, which is dedicated to the violent overthrow of the Egyptian government, has supplied al-Qaeda with some of its senior members, including Osama bin Laden’s top deputy, Ayman al-Zawahri, and the man who orchestrated the Sept. 11 terrorist attacks, Mohammed Atta.

CSIS claims Mr. Mahjoub took part in decision-making on terrorist operations organized by the Vanguards.

Mr. Mahjoub has been convicted in absentia in Egypt for his involvement with the group and sentenced to 15 years in prison. His lawyer, Barbara Jackman, has said his conviction should be disregarded by Canadian courts since Amnesty International has deemed the process “grossly unfair.”

Mr. Mahjoub, who married a Canadian citizen and has two Canadian-born sons, admits he met Mr. bin Laden several times. Mr. Mahjoub worked in a senior capacity at Mr. bin Laden’s agricultural firm in Sudan in the early 1990s, but maintains that he left the job over a wage dispute and has never had contact with him since.

When he arrived in Canada in 1995, Mr. Mahjoub lived for three weeks with Ahmed Said Khadr, the highest-ranking Canadian in al-Qaeda. He initially denied knowing Mr. Khadr in an interview with CSIS.

During Mr. Mahjoub’s successful refugee hearing in Canada, he said he was tortured while detained in Egypt in 1986. He said he was held because his name and phone number appeared on a piece of paper held by another detainee, an old schoolmate. He left Egypt in 1991 and never returned.