If the Conservative government refuses to amend the bill to address those concerns, Trudeau says Liberals will still support it — but will fix the flaws should they win the coming election.
"The current government can accept that Canadians want greater oversight and accountability, or it will give us the opportunity to offer that directly to Canadians in the upcoming election campaign," the Liberal leader said Wednesday.
The New Democrats have also pressed the government to amend the bill by bolstering oversight of security agencies.
Still, NDP public safety critic Randall Garrison accused the Liberals of rushing to a decision on the legislation and said New Democrat MPs will consult constituents during the coming parliamentary break week.
"We're raising the concerns that we have and asking the government some very serious questions about what they intend to do before we decide how we're going to vote on this very important bill," Garrison said Wednesday.
Liberals want the bill amended to provide for parliamentary oversight of security agencies and a mechanism to require mandatory review of the legislation in the future.
The bill would give the Canadian Security Intelligence Service more power to thwart suspected terrorists' travel plans, disrupt bank transactions and covertly interfere with radical websites.
It would also make it easier for the RCMP to obtain a peace bond to restrict the movements of suspects and extend the length of time they can be kept in preventative arrest and detention.
And it would create a new criminal offence: encouraging someone to carry out a terrorist attack.
Trudeau said Liberals welcome measures to build on the powers of preventative arrest, expand the no-fly regime and enhance co-ordinated information sharing among government departments and agencies.
But he added: "I believe that when a government asks its citizens to give up even a small portion of their liberty, it is that government's highest responsibility to guarantee that its new powers will not be abused.
"It is not enough ... for a government to say simply, 'Trust us.' That trust must be earned. It must be checked and it must be renewed."
Prime Minister Stephen Harper has repeatedly brushed off demands for parliamentary oversight, maintaining that sufficient watchdog mechanisms already exist. He repeated that Wednesday in the House of Commons in response to pressure from NDP Leader Tom Mulcair, adding that the bill enhances accountability through the courts.
By promising to support the bill but fix it later, Liberals hope to immunize themselves from Conservative attacks that they're soft on terrorism.
Trudeau's popular support has slid somewhat since he chose last fall to oppose Canada's participation in international airstrikes against Islamic extremists in Iraq.
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