OTTAWA -- Planned new powers for Canada's spy agency seem scarier than they really are, says Prime Minister Stephen Harper's national security adviser.

Giving the Canadian Security Intelligence Service the ability to disrupt extremist plots will help squelch such dangerous activity at a very early stage, Dick Fadden told the Senate national security committee on Monday.

Opponents of the government's anti-terrorism bill have denounced the idea of allowing the spy service to go beyond gathering information to actively derailing suspected schemes.

The new disruption powers could permit CSIS to thwart travel plans, cancel bank transactions and covertly interfere with radical websites.

With its new mandate, CSIS would need "reasonable grounds to believe" there was a security threat before taking measures to disrupt it. The spy agency would require a court warrant whenever proposed disruption measures violate the charter of rights or otherwise breach Canadian law.

Fadden, a former CSIS director, said the bill would help security agencies take "a more surgical approach" to dealing with jihadi-inspired radicals and other threats.

For instance, it would give CSIS explicit power to alert the family of a suspected extremist -- something it can't do now. It would also hand the spy agency more options to manage a shipment of goods destined for a nation that intended to use it to create a weapon of mass destruction, Fadden said.

"If they can find the wherewithal to change the technology, alter it, destroy it on its way across the country, that sort of thing is very, very useful."

Otherwise, the shipment would arrive in the rogue nation and "somebody else has to deal with the problem," said Fadden, who tried to dispel the notion the new powers would be used to target everyone including "the Girl Guides."

"There has to be an actual threat to national security," he said. "This is taken really very seriously.

"It seems more frightening than it really is."

The legislation would also permit greater sharing of security information among federal agencies -- a move Fadden said will help with various kinds of investigations.

Civil libertarians, environmental groups and others -- including the federal privacy commissioner -- have expressed grave concerns about the information-sharing provisions, saying they could open the door to abuses.

John Bennett, executive director of The Sierra Club of Canada, told the senators the environmental organization "could easily find itself engulfed in secret investigations" under the bill's provisions.

"It's already happened."

He cited the recent leak of an RCMP intelligence assessment, Criminal Threats to the Canadian Petroleum Industry, that said those within the anti-oil movement are willing to use "direct action tactics, such as civil disobedience, unlawful protests, break-and-entry, vandalism and sabotage."

Bennett said The Sierra Club, which is named in the report, does not condone violence and has protested the assessment's characterization to the RCMP.

The government insists the bill will not be used to trample on the rights of protesters, but Bennett remains concerned.

"It's just too wide," he said. "It's using a bulldozer to catch ants."

A plan to deal with the seduction of young minds by Islamic extremists is "missing severely" from the Canadian strategy, said Hara Rafiq, managing director of the London-based Quilliam Foundation, which aims to challenge radical narratives.

"This bill will not combat radicalization," he told the senators.