HAY RIVER, N.W.T. -- Stephen Harper left the door open Friday for a re-elected Conservative government to join Washington's controversial ballistic missile defence program, an initiative rejected almost a decade ago by Paul Martin's Liberals amid fierce NDP opposition.

The notion quietly resurfaced two years ago and since then has been endorsed by a Conservative-dominated Senate defence committee with the backing of two former Liberal defence ministers.

Speaking Friday, Harper seemed to lay down a new condition, saying a re-elected Conservative government would only give the green light to ballistic missile defence if it felt Canada's security was in jeopardy.

"Our position is that we keep evaluating our options. If we felt that at any point in time that we faced particular threats that required us to participate, that is something we would look at," Harper said.

"At the present time, we haven't made that assessment."

Previously, the government had said it was waiting for the results of a House of Commons committee study on the matter.

Originally conceived in the 1980s and known as "Star Wars" under then-U.S. President Ronald Reagan, the system has evolved beyond North American protection against intercontinental ballistic missiles to a series of worldwide regional defence plans that include concepts such as Israel's Iron Dome, which was used to shoot down Hamas rockets.

Harper's comments are also noteworthy in light of the growing behind-the-scenes dialogue between Canadian and the U.S. militaries about the potential threats of a rogue cruise missile strike on North America, launched from the Arctic.

The Americans have been asking for multi-purpose sensors in Canada's Arctic that would sniff out a wider range of potential threats. Access to information records show both countries have stepped up intelligence gathering in the North.

NATO warned in April that more than 30 countries either already have -- or were acquiring -- ballistic missile technology that could drop conventional warheads or "weapons of mass destruction" on allies of the military alliance.

While there is no immediate risk, NATO said the alliance "has a responsibility to take this into account as part of its core task of collective defence."

Harper has long made the North a key component of his nine years in office, often using it as backdrops for photo ops and announcements that have a military theme.

Those pictures projecting Canada's military presence in the North are often paired with Harper's tough talk -- especially during the second week of the campaign -- against Russia and its leader, Vladimir Putin.

The Russians have embarked on a determined military buildup in the Arctic, reopening Cold War airfields and positioning at least two combat brigades in a show of force. They have also resumed long-range bomber and ballistic submarine patrols.

Despite the flexing of muscles, Harper says Canada's northern military strategy will not be reset or updated from its initial vision in 2007.

Harper said his government has made investments, such as an army training centre in Resolute Bay and the planned Nanisivik naval dock, "to make sure we can actually protect that sovereignty."

Even though the vast majority of the military projects are years behind schedule, Harper made sure to underline that it was his government that first identified the threat of a resurgent Russia.

"We are making those investments precisely because those and other threats have existed and we have understood for some time now, long before the invasion of Ukraine, that Mr. Putin's Russia was on a very aggressive course in the world," Harper said.

Harper also promised that a re-elected Conservative government would pay the entire cost of paving a stretch of a scenic highway in the Northwest Territories.

Highway 5 connects Fort Smith to Hay River through Wood Buffalo National Park, but much of it is gravel, making for sometimes difficult driving conditions.

Harper said that if re-elected, the Conservatives will provide $14 million to pave a 68-kilometre stretch of the highway, widen some sections and replace drainage culverts.

Normally, the federal government would only chip in one-third of the construction cost for such a project, with the territorial government and local government splitting the remaining two-thirds.

Small towns in the North could take years to raise the necessary funds, the Conservatives argue, which is why they would cover the full cost.

In Iqaluit, Harper promised that if re-elected the party would increase the number of Junior Canadian Rangers to 5,000 by 2018, matching the same increase for the adult program.

There are currently about 4,400 Junior Rangers in 135 patrols across remote and isolated communities in the North. Participants are aged 12 to 18 and learn skills full-fledged Rangers use, such as first aid, hunting, fishing and safeguarding the environment.

The Rangers number 5,000 across 200 communities and are a part of the military reserve. They patrol sparsely settled areas of the North, collecting data, doing surveillance, and helping communities in times of need.

Harper promised that the Rangers would be allowed to keep their Lee Enfield rifles, which are being phased out in favour of the bolt-action, magazine-fed rifle. The switchover is scheduled to start next year and be complete by late-2019.

-- With files from Murray Brewster in Ottawa