Bloc Québécois Leader Gilles Duceppe and NDP Leader Jack Layton took turns in the House of Commons Monday questioning Martin's intentions regarding the proposed anti-missile defence shield.

The issue is not on the official agenda but it's expected to come up in private discussions.

Ottawa still hasn't declared whether it will get involved in the plan.

Although Martin said Monday that his government opposes the weaponization of space, he was vague on Canada's commitment to the anti-missile shield, saying it was "premature" to discuss the details.

Layton criticized Martin's response on the issue, saying "discussing the defence shield at the same time as opposing weapons in space, it's a little like eating a Big Mac and suggesting that you're a vegetarian."

David Rudd, a professor at the Canadian Institute for Strategic Studies in Toronto, said Martin should be more specific.

"Canada, or at least the government, is in the very unusual position of rhetorically opposing something that is not actually prohibited under international law."

The Outer Space Treaty the United States signed with the former Soviet Union in 1967 allows weapons in space, but not weapons of mass destruction.

Joe Varner, a Canadian who teaches at the American Military Institute in Washington, said the militarization of space has been going on since the 1950s.

"What they really should be doing is looking at new treaties, new international agreements to make sure that what has become the gradual weaponization of space is restricted."

Meanwhile Peter Boag, president of the Aerospace Industries Association, said he is worried about the consequences of not signing on to the U.S. missile defence program.

"How Canada is perceived in the U.S. and how our foreign policies allign with those of the U.S. do have an impact on our trade relationship and on the market access for Canadian firms in the U.S," he said.

But it was - and that's likely to stoke the political fires under the controversial issue. Talks between Bush and Prime Minister Paul Martin were to have covered a range of topics, from mad cow disease to border security. But missile defence wasn't on the list outlined by officials.

Bush said however that it did come up.

"We also discussed ways to strengthen the security partnership that for more than six decades has helped to keep this continent peaceful and secure," he told a news conference following his meeting with Martin.

"We talked about the future of Norad and how that organization can best meet emerging threats and safeguard our continent against attack from ballistic missiles."

A Canadian spokesman said later that the president simply outlined why he backs missile defence and didn't link it to Norad, the 50-year-old Canada-U.S. defence pact.

"He also indicated that he understands that there's a debate taking place in Canada and that he respects that," the official said on condition of anonymity.

"The prime minister, for his part, essentially said, 'There is a debate taking place. We've made a commitment that we will consult Parliament and then we'll move forward or not on that basis'."

The official said Bush understands there's a political debate over the issue in Canada and that he wasn't trying to push for a decision on whether Canada would join the program.

Martin has long downplayed missile defence. He says there is no U.S. pressure for Canada to join the missile shield plan. Nor, he says, is there any deadline for a decision.

But the project was clearly on Bush's agenda.

Missile defence has prompted demonstrations, speeches in Parliament and books and articles galore over the past year or so.

The United States is in the process of deploying a handful of interceptor missiles in Alaska and California, which together with powerful radars in Alaska, Greenland and Britain, are the heart of the system.

They say it's designed to protect North America against an accidental launch of a nuclear missile or against a deliberate, small-scale strike from some "rogue" nation.

Opponents condemn the idea. They say it's too expensive, it won't work and will promote a new arms race leading inevitably to weapons in space.

Supporters, and even some on the fence, express doubts about all or some of these concerns.

But the issue has become highly political.

The NDP and the Bloc Quebecois are solidly opposed. Even some in Martin's own caucus are dubious about the idea.

The Conservatives, while generally supportive of closer ties with the United States, say they want to see the details of a missile-defence agreement before taking a stand.

The government has promised a vote in the Commons on the issue, but it's not clear when that might be and it won't be binding on the government.