TORONTO - Secret evidence against suspected terrorist Abdullah Khadr should be made public to ensure he gets a fair extradition hearing despite government concerns such disclosure could threaten Canada's national security, an Ontario court heard Tuesday.

Government lawyers argued for secrecy, saying the country's safety outweighed constitutional rights to transparent justice and the public's right to know.

"National security is a legitimate public interest of the highest order," Crown lawyer Matthew Sullivan told Superior Court Justice Christopher Speyer.

"The stakes are very high."

Khadr, 27, a Canadian citizen, is fighting extradition to the United States, where he is wanted on charges of buying weapons for al-Qaida to be used against American soldiers in Afghanistan.

He argues he was tortured, during 14 months in custody in Pakistan, into making incriminating statements to American and Canadian investigators.

Some of the evidence -- including documents that revealed the Americans paid the Pakistanis a $500,000 bounty to capture him despite knowing he risked serious mistreatment -- has already been made public under a previous Federal Court order.

Other material, which Khadr's lawyers say help his case, has been off-limits to the public although a summary was released to the defence and the accused.

Public scrutiny of witnesses from the intelligence community who might testify about that information is essential to keep them honest, said lawyer Nate Whitling.

"I'm not going to say they would lie (behind closed doors) but there is less of an encouragement to be completely truthful," Whitling said.

The lawyer also argued it would be inherently "unfair" to allow Khadr testify in the public spotlight while government witnesses remain in the shadows.

Sullivan argued that the safety of citizens, national institutions and Canada's Armed Forces are all at risk if the material from the Canadian Security Intelligence Service, RCMP and Dept. of Foreign Affairs is disclosed.

"The harm in this case is not theoretical. It is actual harm."

He also said the "third-party rule" -- that information supplied by foreign countries be kept secret -- should be considered "sacred."

It's not just a matter of embarrassing foreign governments, said Sullivan, who added the flow of critical intelligence could be upset.

"Canada relies on its foreign allies for security information," he told Speyer.

For his part, Whitling noted the rule is often breached.

He cited the public inquiry into the American rendition of Canadian Maher Arar to torture in Syria, disclosure of the bounty despite American objections, and the release of videotapes of Canada's spy agency interrogating Khadr's younger brother Omar in Guantanamo Bay.

Part of Tuesday's proceedings were held behind closed doors as the two sides wrangled over the secret evidence and witnesses who might be called to testify during the extradition trial.

The eldest son in Canada's notorious Khadr family has been in custody in Toronto since his arrest at American request 2 1/2 years ago.

He was denied bail last month when a judge ruled he still posed a significant danger to public safety despite his lengthy incarceration.