(Adds remarks on active discussions, paragraphs 7-8)
OTTAWA, June 5 Canada has not changed its position on not joining the U.S. missile defense shield, but is examining its stance given changing global circumstances, Prime Minister Stephen Harper said on Thursday.
Speaking in Brussels at the end of a meeting of the Group of Seven leading industrialized nations, which was dominated by the crisis in Ukraine, Harper said Canada regularly examined defense policies, including the missile shield.
"It was our judgment in the past that Canadians did not need the security of participation in the anti-ballistic missile defense system," the Conservative prime minister said.
"Obviously there are changes occurring in the world and we will continue to examine whether that does or does not serve Canadian interests and we'll make whatever decisions are in the best security safety interests of Canadians, but obviously at the moment, we have not decided to revise the position."
The previous Liberal government had decided in 2005 under Prime Minister Paul Martin against joining the shield, at a time when then-U.S. President George W. Bush was not popular within the Canadian government.
But two former Liberal defense ministers, Bill Graham and David Pratt, urged the Conservative government in Senate committee last month to join the program.
Riki Ellison, founder of the non-profit Missile Defense Advocacy Alliance, welcomed Harper's remarks and said there were active discussions by U.S. and Canadian officials about integrating Canada into the U.S. ballistic missile defense system.
He said one proposal called for Canada to invest about $100 million to join the defense system. Another proposal would see Canada add radar and other early warning sensors to its new ships, which would help augment the United States' ability to track possible incoming missiles on both the Atlantic and Pacific coasts.
Part of Canada's calculation in not investing in the defense shield had been that with its main cities close to the U.S. border, it would already be effectively covered to a large extent.
The thinking went that missiles heading in the general direction of Vancouver, British Columbia, for example, would likely be targeted anyway by U.S. defenses protecting Seattle, Washington, just 120 miles (193 km) to the south.
The system is still in the process of being tested and improved upon, and is not yet fail-safe, but advocates say it is important to try to defend against possible threats from countries like North Korea and Russia. (Reporting by Randall Palmer in Ottawa, additional reporting by Andrea Shalal in Washington; Editing by Sofina Mirza-Reid and G Crosse)