TORONTO - Canadian officials are trying to deport a highly trained Sikh terrorist assigned to kill senior Indian government officials, including a Cabinet minister, but the government's effort has been hampered by fears the assassin might be tortured.

The man, who goes by the name Bachan Singh Sogi and many other aliases, is a member of the Babbar Khalsa International, the violent Sikh separatist group believed responsible for the 1985 Air-India bombing that killed 329 people, most of them Canadians.

Mr. Sogi, 43, flew to Toronto seeking refugee status and lived in Montreal for more than a year before he was arrested in August, 2002. Intelligence and Immigration officials had determined he was a terrorist better known as Gurnham Singh and Piare.

The Canadian Security Intelligence Service (CSIS) said it had corroborated reports that Mr. Sogi was a trained explosives and weapons expert who was planning to assassinate Prakash Singh Badal, Chief Minister of Punjab, and his son Sikhbir Singh Badal.

Also on his target list was K.P.S. Gill, the former Punjab police chief, who led India's anti-terrorism campaign against such Sikh extremist factions as the Babbar Khalsa and who is credited with bringing an end to separatist violence in the western state.

Despite the seriousness of the government's allegations against Mr. Sogi and the continuing focus on Sikh terrorism at the Air-India trial in Vancouver, the arrest has so far escaped public attention.

He remains in custody and has denied the allegations.

The Immigration and Refugee Board, however, which was privy to secret intelligence information, ruled he should be deported on grounds of national security, and the Federal Court of Canada upheld the decision. But the case has become the latest challenge for the Canadian immigration system, which critics contend is unable to get rid of even known terrorists because it allows refugee lawyers to fend off deportation by filing repeated court appeals.

The Supreme Court of Canada ruled in 2002 that terrorists caught in Canada who fear they might be tortured in their homelands can only be deported if they pose a significant threat to Canadians, a ruling that some say cemented Canada's role as a safe haven.

The Immigration Department determined in June, 2003, that Mr. Sogi "would be at risk of torture if deported to India." But in August, another assessment said he was "a present and future danger to the security of Canada."

An immigration official weighed the two reports and determined he should be deported regardless of the torture risk. By accepting an assassination assignment, Mr. Sogi had shown he was directly and intimately involved in Sikh terrorism, the official wrote.

"The overall interests of Canada and Canadian security must be given paramount consideration in this instance. In my view, the presence in Canada of terrorists, terrorist groups and terrorism in general is an anathema to the values and beliefs of Canadians.

"It would be unconscionable to allow him to remain in Canada."

But Mr. Sogi's lawyers filed an appeal and last month a Federal Court judge ruled the deportation decision was flawed. Judge Sandra Simpson said the government had not considered Mr. Sogi's offer to observe a curfew and wear a tracking device in order to avoid deportation.

"In my view, a decision to deport to torture must consider, in the balancing exercise, any alternatives proposed to reduce the threat. I have concluded that, in the unusual circumstances of this case, it was patently unreasonable to decide to deport the applicant without considering the applicant's proposal," she wrote.

The government also erred by assuming that because of Mr. Sogi's terrorist "history and credentials, he is automatically a serious threat to national security." She ordered the Immigration department to revisit the deportation decision and report back by Sept. 30.

The Babbar Khalsa (BK) and Babbar Khalsa International (BKI) were among the first international terroris t groups to use Canada as a base for global violence. According to a report by Canada's Department of Public Safety, the groups were created to fight India for an independent Sikh state to be called Khalistan.

"BK and BKI continue to be one of the most vicious and powerful of the militant Sikh groups," the report said.

Past leaders include Canadians Talwinder Singh Parmar, alleged mastermind of the Air-India bombing, and Ajaib Singh Bagri, who is on trial for his alleged role in the attack.